Zoom lens, optical apparatus, and method for manufacturing zoom lens

ABSTRACT

A zoom lens includes, in order from an object side along an optical axis, a first lens group G 1  having positive refractive power, a second lens group G 2  having negative refractive power, and a third lens group G 3  having positive refractive power. Upon zooming from a wide-angle end state W to a telephoto end state T, a distance between the first lens group G 1  and the second lens group G 2  increases, and a distance between the second lens group G 2  and the third lens group G 3  decreases. Given conditions are satisfied. Accordingly, a zoom lens having high optical performance with suppressing variations in aberrations, an optical apparatus equipped therewith, and a method for manufacturing the zoom lens are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 16/237,601 filedDec. 31, 2018, which is now U.S. Pat. No. 10,895,721, which is adivision of application Ser. No. 15/359,227 filed Nov. 22, 2016, whichis now U.S. Pat. No. 10,203,488, and which is a division of applicationSer. No. 13/194,890 filed Jul. 29, 2011, which is now U.S. Pat. No.9,523,843.

This application also claims the benefit of priority from the followingJapanese patent applications, the disclosures of which are hereinincorporated by reference:

-   Japanese Patent Application No. 2010-171323 filed on Jul. 30, 2010;-   Japanese Patent Application No. 2010-171324 filed on Jul. 30, 2010;-   Japanese Patent Application No. 2010-171336 filed on Jul. 30, 2010;-   Japanese Patent Application No. 2011-097333 filed on Apr. 25, 2011;-   Japanese Patent Application No. 2011-151892 filed on Jul. 8, 2011;-   Japanese Patent Application No. 2011-151899 filed on Jul. 8, 2011;    and-   Japanese Patent Application No. 2011-151906 filed on Jul. 8, 2011.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a zoom lens, an optical apparatusequipped therewith, and a method for manufacturing the zoom lens.

Related Background Art

A lot of zoom lenses having a lens group with a positive refractivepower disposed to the most object side have been proposed (for example,see Japanese Patent Application Laid-Open No. 2008-003195). Regardingsuch a zoom lens, request for suppressing ghost images and flare, whichdeteriorate optical performance, and aberrations become increasinglystrong. Accordingly, a higher optical performance is required toantireflection coatings applied to a lens surface, so that in order tomeet such request, multilayer design technology and multilayer coatingtechnology are continuously progressing (for example, see JapanesePatent Application Laid-Open No. 2000-356704).

When a conventional zoom lens is forcibly made to have a higher zoomratio, variation in aberrations increases, so that sufficiently highoptical performance cannot be obtained. In addition, there is a problemthat reflection light producing ghost images and flare is liable to begenerated from optical surfaces in such a zoom lens.

SUMMARY OF THE INVENTION

The present invention is made in view of the above-described problems,and has an object to provide a zoom lens having excellent opticalperformance with suppressing variations in various aberrations, andghost images and flare, an optical apparatus equipped therewith, and amethod for manufacturing the zoom lens.

According to a first aspect of the present invention, there is provideda zoom lens comprising, in order from an object along an optical axis: afirst lens group having positive refractive power; a second lens grouphaving negative refractive power; and a third lens group having positiverefractive power, upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increasing, and a distance between the second lensgroup and third lens group decreasing, the first lens group including apositive lens A that satisfies the following conditional expression (1):85.0<νdA  (1)where νdA denotes an Abbe number at d-line of a material of the positivelens A in the first lens group, and

the following conditional expression (2) being satisfied:3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

According to a second aspect of the present invention, there is providedan optical apparatus equipped with the zoom lens according to the firstaspect.

According to a third aspect of the present invention, there is provideda zoom lens comprising, in order from an object along an optical axis: afirst lens group having positive refractive power; a second lens grouphaving negative refractive power; and a third lens group having positiverefractive power, upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increasing, and a distance between the second lensgroup and third lens group decreasing, the zoom lens including apositive lens A′ that satisfies the following conditional expressions(14) and (15):1.540<ndA′  (14)66.5<νdA′  (15)where ndA′ denotes a refractive index of a material of the positive lensA′, and νdA′ denotes an Abbe number of the material of the positive lensA′, and the following conditional expression (2) being satisfied:3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

According to a fourth aspect of the present invention, there is providedan optical apparatus equipped with the zoom lens according to the thirdaspect.

zoom lens comprising, in order from an object along an optical axis: afirst lens group having positive refractive power; a second lens grouphaving negative refractive power; and a third lens group having positiverefractive power, upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increasing, and a distance between the second lensgroup and third lens group decreasing, the first lens group including aplurality of positive lenses A″ that satisfies the following conditionalexpression (22):66.5<νdA″ when 1.540≤ndA″75.0<νdA″ when ndA″≤1.540  (22)where ndA″ denotes a refractive index at d-line of a material of each ofa plurality of positive lenses in the first lens group, νdA″ denotes anAbbe number at d-line of a material of each of the plurality of positivelenses in the first lens group, and the following conditionalexpressions (23) and (3) being satisfied:4.75<f1/fw<11.0  (23)0.28<f1/ft<0.52  (3)where fw denotes a focal length of the zoom lens in the wide-angle endstate, ft denotes a focal length of the zoom lens in the telephoto endstate, and f1 denotes a focal length of the first lens group.

According to a sixth aspect of the present invention, there is providedan optical apparatus equipped with the zoom lens according to the fifthaspect.

According to a seventh aspect of the present invention, there isprovided a method for manufacturing a zoom lens including, in order froman object side along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power, the methodcomprising steps of: disposing the first lens group, the second lensgroup and the third lens group movably such that a distance between thefirst lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases;disposing a positive lens A satisfying the following conditionalexpression (1):85.0<νdA  (1)where νdA denotes an Abbe number at d-line of a material of the positivelens A in the first lens group; and disposing each lens with satisfyingthe following conditional expression (2):3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

According to a eighth aspect of the present invention, there is provideda method for manufacturing a zoom lens including, in order from anobject side along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power, the methodcomprising steps of: disposing the first lens group, the second lensgroup and the third lens group movably such that a distance between thefirst lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases;disposing a positive lens A′ satisfying the following conditionalexpressions (14) and (15):1.540<ndA′  (14)66.5<νdA′  (15)where ndA′ denotes a refractive index of a material of the positive lensA′, and νdA′ denotes an Abbe number of the material of the positive lensA′, and

disposing each lens with satisfying the following conditional expression(2):3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

According to a ninth aspect of the present invention, there is provideda method for manufacturing a zoom lens including, in order from anobject side along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power, the methodcomprising steps of: disposing the first lens group, the second lensgroup and the third lens group movably such that a distance between thefirst lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases;disposing a plurality of positive lenses A″ satisfying the followingconditional expression (22):66.5<νdA″ when 1.540≤ndA″75.0<νdA″ when ndA″≤1.540  (22)where ndA″ denotes a refractive index at d-line of a material of each ofthe plurality of positive lenses in the first lens group, νdA″ denotesan Abbe number at d-line of a material of each of the plurality ofpositive lenses in the first lens group, and disposing each lens withsatisfying the following conditional expressions (23) and (3):4.75<f1/fw<11.0  (23)0.28<f1/ft<0.52  (3)

where fw denotes a focal length of the zoom lens in the wide-angle endstate, ft denotes a focal length of the zoom lens in the telephoto endstate, and f1 denotes a focal length of the first lens group.

The present invention makes it possible to provide a zoom lens havingexcellent optical performance with suppressing variations in variousaberrations and ghost images and flare, an optical apparatus equippedtherewith, and a method for manufacturing the zoom lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a lens configuration of a zoom lensaccording to Example 1 of a first embodiment, and Example 4 of a secondembodiment of the present application.

FIGS. 2A, 2B and 2C are graphs showing various aberrations of the zoomlens according to Example 1 of the first embodiment, and Example 4 ofthe second embodiment upon focusing on an infinitely distant object, inwhich FIG. 2A is a wide-angle end state, FIG. 2B is an intermediatefocal length state, and FIG. 2C is a telephoto end state.

FIG. 3 is a sectional view showing the lens configuration of the lenssystem according to Example 1 of the first embodiment, and Example 4 ofthe second embodiment and is an explanatory view, in which light raysreflected from a first-ghost-generating surface are reflected by asecond-ghost-generating surface.

FIG. 4 is a sectional view showing a lens configuration of a zoom lensaccording to Example 2 of the first embodiment of the presentapplication.

FIGS. 5A, 5B and 5C are graphs showing various aberrations of the zoomlens according to Example 2 of the first embodiment upon focusing on aninfinitely distant object, in which FIG. 5A is a wide-angle end state,FIG. 5B is an intermediate focal length state, and FIG. 5C is atelephoto end state.

FIG. 6 is a sectional view showing a lens configuration of a zoom lensaccording to Example 3 of the first embodiment, and Example 8 of thesecond embodiment of the present application.

FIGS. 7A, 7B and 7C are graphs showing various aberrations of the zoomlens according to Example 3 of the first embodiment, and Example 8 ofthe second embodiment upon focusing on an infinitely distant object, inwhich FIG. 7A is a wide-angle end state, FIG. 7B is an intermediatefocal length state, and FIG. 7C is a telephoto end state.

FIG. 8 is a sectional view showing a lens configuration of a zoom lensaccording to Example 5 of the second embodiment, and Example 10 of athird embodiment of the present application.

FIGS. 9A, 9B and 9C are graphs showing various aberrations of the zoomlens according to Example 5 of the second embodiment, and Example 10 ofthe third embodiment upon focusing on an infinitely distant object, inwhich FIG. 9A is a wide-angle end state, FIG. 9B is an intermediatefocal length state, and FIG. 9C is a telephoto end state.

FIG. 10 is a sectional view showing a lens configuration of a zoom lensaccording to Example 6 of the second embodiment, and Example 11 of thethird embodiment of the present application.

FIGS. 11A, 11B and 11C are graphs showing various aberrations of thezoom lens according to Example 6 of the second embodiment, and Example11 of the third embodiment upon focusing on an infinitely distantobject, in which FIG. 11A is a wide-angle end state, FIG. 11B is anintermediate focal length state, and FIG. 11C is a telephoto end state.

FIG. 12 is a sectional view showing a lens configuration of a zoom lensaccording to Example 7 of the second embodiment, and Example 9 of thethird embodiment of the present application.

FIGS. 13A, 13B and 13C are graphs showing various aberrations of thezoom lens according to Example 7 of the second embodiment, and Example 9of the third embodiment upon focusing on an infinitely distant object,in which FIG. 13A is a wide-angle end state, FIG. 13B is an intermediatefocal length state, and FIG. 13C is a telephoto end state.

FIG. 14 is a sectional view showing the lens configuration of the lenssystem according to Example 9 of the third embodiment and is anexplanatory view, in which light rays reflected from afirst-ghost-generating surface are reflected by asecond-ghost-generating surface.

FIG. 15 is a sectional view showing a lens configuration of a zoom lensaccording to Example 12 of the third embodiment of the presentapplication.

FIGS. 16A, 16B and 16C are graphs showing various aberrations of thezoom lens according to Example 12 of the third embodiment upon focusingon an infinitely distant object, in which FIG. 16A is a wide-angle endstate, FIG. 16B is an intermediate focal length state, and FIG. 16C is atelephoto end state.

FIG. 17 is an explanatory view showing a configuration of anantireflection coating according to the present application.

FIG. 18 is a graph showing spectral reflectance of an antireflectioncoating according to the present embodiment.

FIG. 19 is a graph showing spectral reflectance of an antireflectioncoating according to a variation of the present application.

FIG. 20 is a graph showing incident angle dependency of spectralreflectance of the antireflection coating according to the variation.

FIG. 21 is a graph showing spectral reflectance of an antireflectioncoating according to a conventional example.

FIG. 22 is a graph showing incident angle dependency of spectralreflectance of the antireflection coating according to the conventionalexample.

FIG. 23 is a diagram showing a construction of a camera equipped withthe zoom lens according to Example 1 of the first embodiment.

FIG. 24 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the first embodiment.

FIG. 25 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the second embodiment.

FIG. 26 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the third embodiment.

DESCRIPTION OF THE MOST PREFERRED EMBODIMENT First Embodiment

A zoom lens according to a first embodiment of the present applicationis explained below.

The zoom lens according to the first embodiment of the presentapplication includes, in order from an object side along an opticalaxis, a first lens group having positive refractive power, a second lensgroup having negative refractive power, and a third lens group havingpositive refractive power. Upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increases, and a distance between the second lensgroup and the third lens group decreases. With this configuration, itbecomes possible to realize an optical system capable of zooming, and,at the same time, suppress variation in distortion generated uponzooming.

In a zoom lens according to the first embodiment, the first lens groupincludes a positive lens A, which satisfies the following conditionalexpression (1), and the following conditional expression (2) issatisfied:85.0<νdA  (1)3.90<f1/fw<11.00  (2)where νdA denotes an Abbe number at d-line (wavelength λ=587.6 nm) ofthe positive lens A in the first lens group, fw denotes a focal lengthof the zoom lens in the wide-angle end state, and f1 denotes a focallength of the first lens group.

Conditional expression (1) defines an optimum Abbe number of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variation in chromatic aberrationgenerated upon zooming from the wide-angle end state to the telephotoend state.

When the value νdA is equal to or falls below the lower limit ofconditional expression (1), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

Conditional expression (2) defines an appropriate range of the focallength of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state.

When the ratio f1/fw is equal to or falls below the lower limit ofconditional expression (2), refractive power of the first lens groupbecomes strong, so that it becomes difficult to suppress variations inlateral chromatic aberration and off-axis aberrations, in particular,astigmatism. Accordingly, high optical performance cannot be obtained.

On the other hand, when the ratio f1/fw is equal to or exceeds the upperlimit of conditional expression (2), refractive power of the first lensgroup becomes weak, so that in order to obtain a given zoom ratio amoving amount of the first lens group with respect to an image plane hasto increase. As a result, variation in a height from the optical axis ofthe off-axis ray passing through the first lens group becomes large, sothat it becomes difficult to suppress variations in lateral chromaticaberration and off-axis aberrations, in particular, astigmatism.Accordingly, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (2) to 4.75.In order to further secure the effect of the present embodiment, it ismost preferable to set the lower limit of conditional expression (2) to5.10.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (2) to 8.80.In order to further secure the effect of the present embodiment, it ismost preferable to set the upper limit of conditional expression (2) to7.60.

In a zoom lens according to the first embodiment, the followingconditional expression (3) is preferably satisfied:0.28<f1/ft<0.52  (3)where ft denotes a focal length of the zoom lens in the telephoto endstate.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state.

When the ratio f1/ft is equal to or falls below the lower limit ofconditional expression (3), refractive power of the first lens groupbecomes strong, so that it becomes difficult to suppress variations inlongitudinal chromatic aberration and spherical aberration. Accordingly,high optical performance cannot be obtained.

On the other hand, when the ratio f1/ft is equal to or exceeds the upperlimit of conditional expression (3), refractive power of the first lensgroup becomes weak, in order to obtain a given zoom ratio, a movingamount of the first lens group with respect to the image plane has toincrease. As a result, variation in a height from the optical axis ofthe off-axis ray passing through the first lens group becomes large, sothat it becomes difficult to suppress variations in lateral chromaticaberration and off-axis aberrations, in particular, astigmatism.Accordingly, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (3) to 0.31.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (3) to 0.48.In order to further secure the effect of the present embodiment, it ismost preferable to set the upper limit of conditional expression (3) to0.44.

In a zoom lens according to the first embodiment, the followingconditional expression (4) is preferably satisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state, and is for realizinghigh optical performance with suppressing variations in chromaticaberration and off-axis aberrations generated upon zooming.

When the ratio Δ1/f1 is equal to or falls below the lower limit ofconditional expression (4), the moving amount of the first lens groupwith respect to the image plane becomes small, so that in order toobtain a given zoom ratio, refractive power of the first lens group hasto be large. As a result, upon zooming from the wide-angle end state tothe telephoto end state, variation in refractive power according tovariation in the height from the optical axis of the off-axis raypassing through the first lens group becomes large, so that it becomesdifficult to suppress variations in lateral chromatic aberration andoff-axis aberrations, in particular, astigmatism. Accordingly, highoptical performance cannot be obtained.

On the other hand, when the ratio Δ1/f1 is equal to or exceeds the upperlimit of conditional expression (4), the moving amount of the first lensgroup with respect to the image plane becomes large, so that uponzooming from the wide-angle end state to the telephoto end state,variation in the height from the optical axis of the off-axis raypassing through the first lens group becomes large. As a result, itbecomes difficult to suppress variations in lateral chromatic aberrationand off-axis aberrations, in particular, astigmatism. Accordingly, highoptical performance cannot be obtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (4) to 0.36.In order to further secure the effect of the present embodiment, it ismost preferable to set the lower limit of conditional expression (4) to0.48.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (4) to 0.95.

In a zoom lens according to the first embodiment, the followingconditional expression (5) is preferably satisfied:0.65<f1A/f1<1.75  (5)where f1A denotes a focal length of the positive lens A in the firstlens group.

Conditional expression (5) defines an optimum focal length of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming.

When the ration f1A/f1 is equal to or falls below the lower limit ofconditional expression (5), refractive power of the positive lens Abecomes strong, so that upon zooming from the wide-angle end state tothe telephoto end state, variation in refractive power in accordancewith variation in the height of the off-axis ray passing through thepositive lens A becomes large. As a result, it becomes difficult tosuppress variations in lateral chromatic aberration and off-axisaberrations, in particular, astigmatism, so that high opticalperformance cannot be obtained.

On the other hand, when the ration f1A/f1 is equal to or exceeds theupper limit of conditional expression (5), refractive power of thepositive lens A becomes weak, positive refractive power other than thepositive lens A in the first lens group becomes strong, so that uponzooming from the wide-angle end state to the telephoto end state,variation in refractive power in accordance with variation in the heightof the off-axis ray passing through the positive lens A becomes large.As a result, it becomes difficult to suppress variations in lateralchromatic aberration and off-axis aberrations, in particular,astigmatism, so that high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (5) to 0.80.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (5) to 1.35.

In a zoom lens according to the first embodiment, the followingconditional expression (6) is preferably satisfied:1.75<φ1A/fw<4.50  (6)where φ1A denotes an effective diameter of the positive lens A in thefirst lens group.

Conditional expression (6) defines an optimum effective diameter of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming.

When the ratio φ1A/fw is equal to or falls below the lower limit ofconditional expression (6), upon zooming from the wide-angle end stateto the telephoto end state, variation in the height from the opticalaxis of the off-axis ray passing through the positive lens A in thefirst lens group becomes small. As a result, it becomes difficult tosuppress variations in off-axis aberrations, in particular, astigmatism,so that high optical performance cannot be obtained.

On the other hand, when the ratio φ1A/fw is equal to or exceeds theupper limit of conditional expression (6), upon zooming from thewide-angle end state to the telephoto end state, variation in the heightfrom the optical axis of the off-axis ray passing through the positivelens A in the first lens group becomes large. As a result, it becomesdifficult to suppress variations in lateral chromatic aberration andoff-axis aberrations, in particular, astigmatism, so that high opticalperformance cannot be obtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (6) to 2.45.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (6) to 3.80.

In a zoom lens according to the first embodiment, the first lens grouppreferably includes a positive lens B, which satisfies the followingconditional expression (7):1.580<ndB  (7)where ndB denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of the positive lens B in the first lens group.

Conditional expression (7) defines an optimum refractive index of thematerial of the positive lens B in the first lens group, and is forrealizing high optical performance with suppressing variations inoff-axis aberrations generated upon zooming.

When the value ndB is equal to or falls below the lower limit ofconditional expression (7), curvature of the surface of the positivelens B becomes strong, so that upon zooming from the wide-angle endstate to the telephoto end state, variation in the deviation angle inaccordance with variation in the height from the optical axis of theoff-axis ray passing through the positive lens B becomes large. As aresult, it becomes difficult to suppress variations in off-axisaberrations, in particular, astigmatism, so that high opticalperformance cannot be obtained.

In a zoom lens according to the first embodiment, the first lens grouppreferably includes a positive lens B, which satisfies the followingconditional expression (8):40.0<νdB<66.5  (8)where νdB denotes an Abbe number at d-line (wavelength λ=587.6 nm) of amaterial of the positive lens B in the first lens group.

Conditional expression (8) defines an optimum Abbe number of thematerial of the positive lens B in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming.

When the value νdB is equal to or falls below the lower limit ofconditional expression (8), dispersion of the material of the positivelens B becomes large, so that upon zooming from the wide-angle end stateto the telephoto end state, variation in dispersion in accordance withvariation in the height from the optical axis of the off-axis raypassing through the positive lens B becomes large. As a result, itbecomes difficult to suppress variation in lateral chromatic aberration,so that high optical performance cannot be obtained.

On the other hand, when the value νdB is equal to or exceeds the upperlimit of conditional expression (8), dispersion of the material of thepositive lens B becomes small, so that when a negative lens is includedin the first lens group, correction of chromatic aberration becomesexcessive. As a result, it becomes difficult to suppress variation inlateral chromatic aberration. When a negative lens is not included inthe first lens group, since chromatic aberration remains, variation inchromatic aberration becomes difficult to suppress, so that high opticalperformance cannot be obtained. Accordingly, in either case, highoptical performance cannot be realized.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (8) to 49.0.

In a zoom lens according to the first embodiment, the followingconditional expression (9) is preferably satisfied:0.65<f1B/f1<1.75  (9)where f1B denotes a focal length of the positive lens B in the firstlens group.

Conditional expression (9) defines an optimum focal length of thepositive lens B in the first lens group.

When the ratio f1B/f1 is equal to or falls below the lower limit ofconditional expression (9), refractive power of the positive lens Bbecomes strong, so that upon zooming from the wide-angle end state tothe telephoto end state, variation in refractive power in accordancewith variation in the height from the optical axis of the off-axis raypassing through the positive lens B becomes large. As a result, itbecomes difficult to suppress variations in lateral chromatic aberrationand off-axis aberrations, in particular, astigmatism, so that highoptical performance cannot be realized.

On the other hand, when the ratio f1B/f1 is equal to or exceeds theupper limit of conditional expression (9), refractive power of thepositive lens B becomes weak, so that refractive power of the positivelens other than the positive lens B in the first lens group becomesstrong. As a result, upon zooming from the wide-angle end state to thetelephoto end state, variation in refractive power in accordance withvariation in the height from the optical axis of the off-axis raypassing through the positive lens B becomes large. Accordingly, itbecomes difficult to suppress variations in lateral chromatic aberrationand off-axis aberrations, in particular, astigmatism, so that highoptical performance cannot be realized.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (9) to 0.77.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (9) to 1.42.

In a zoom lens according to the first embodiment, the followingconditional expression (10) is preferably satisfied:1.75<φ1B/fw<4.50  (10)where φ1B denotes an effective diameter of the positive lens B in thefirst lens group.

Conditional expression (10) defines an optimum diameter of the positivelens B in the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming.

When the ratio φ1B/fw is equal to or falls below the lower limit ofconditional expression (10), upon zooming from the wide-angle end stateto the telephoto end state, variation in the height from the opticalaxis of the off-axis ray passing through the positive lens B in thefirst lens group becomes small, so that it becomes difficult to suppressvariations in off-axis aberrations, in particular, astigmatism.Accordingly, high optical performance cannot be realized.

On the other hand, when the ratio φ1B/fw is equal to or exceeds theupper limit of conditional expression (10), upon zooming from thewide-angle end state to the telephoto end state, variation in the heightfrom the optical axis of the off-axis ray passing through the positivelens B in the first lens group becomes large, so that it becomesdifficult to suppress variations in lateral chromatic aberration andoff-axis aberrations, in particular, astigmatism. Accordingly, highoptical performance cannot be realized.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (10) to2.45.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (10) to3.80.

In a zoom lens according to the first embodiment, the first lens grouppreferably includes a negative lens which satisfies the followingconditional expressions (11) and (12):1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state.

When the value νdN is equal to or falls below the lower limit ofconditional expression (11), curvature of the surface of the negativelens in the first lens group becomes large, so that upon zooming fromthe wide-angle end state to the telephoto end state, variations inoff-axis aberrations, in particular, astigmatism in accordance withvariation in the height from the optical axis of the off-axis raypassing through the negative lens become difficult to be suppressed.Accordingly, high optical performance cannot be realized.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (11) to1.780.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state.

When the value νdN is equal to or falls below the lower limit ofconditional expression (12), it becomes difficult to suppress variationin second order chromatic aberration generated upon zooming from thewide-angle end state to the telephoto end state, so that high opticalperformance cannot be realized.

On the other hand, when the value νdN is equal to or exceeds the upperlimit of conditional expression (12), and when a given achromatizationis to be carried out in the first lens group, refractive power of eachof the positive lens and the negative lens becomes large. As a result,variations in off-axis aberrations, in particular, astigmatism inaccordance with variation in the height from the optical axis of theoff-axis ray passing through the negative lens upon zooming from thewide-angle end state to the telephoto end state become difficult to besuppressed, so that high optical performance cannot be realized.

In order to secure the effect of the present embodiment, it ispreferable to set the upper limit of conditional expression (12) to43.0.

In a zoom lens according to the first embodiment, the first lens groupis preferably composed of one negative lens and two positive lenses.

With this configuration, the thickness of the first lens group can besuppressed. Accordingly, upon zooming from the wide-angle end state tothe telephoto end state, variation in the height from the optical axisof the off-axis ray passing through the most object side surface of thefirst lens group can be suppressed, so that variations in off-axisaberrations, in particular, astigmatism can be suppressed. As a result,high optical performance can be realized.

In a zoom lens according to the first embodiment, the third lens grouppreferably includes a positive lens, which satisfies the followingconditional expression (13):65.5<νd3 when 1.540≤nd375.0<νd3 when nd3<1.540  (13)where nd3 denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a positive lens in the third lens group, and νd3denotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the positive lens in the third lens group.

Conditional expression (13) defines an optimum Abbe number of thematerial of the positive lens in the third lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state.

When the value νd3 is equal to or falls below the lower limit ofconditional expression (13), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

In order to secure the effect of the present embodiment, it ispreferable to set the lower limit of conditional expression (13) to 67.5when 1.540 nd3. In order to secure the effect of the present embodiment,it is preferable to set the lower limit of conditional expression (13)to 80.5 when nd3<1.540.

In a zoom lens according to the first embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power and a rear lens group havingpositive refractive power, and a distance between the front lens groupand the rear lens group decreases upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens according to the first embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power, a middle lens group havingnegative refractive power, and a rear lens group having positiverefractive power, and a distance between the front lens group and themiddle lens group varies, and a distance between the middle lens groupand the rear lens group varies upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens according to the first embodiment, it is preferable thata distance between the front lens group and the middle lens groupincreases, and a distance between the middle lens group and the rearlens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

Then, a zoom lens seen from another point of view according to the firstembodiment of the present application includes, in order from an objectside along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power. Upon zoomingfrom a wide-angle end state to a telephoto end state, a distance betweenthe first lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases,thereby realizing an optical system capable of zooming and, at the sametime, suppressing variation in distortion upon zooming.

In a zoom lens seen from another point of view according to the firstembodiment, the first lens group includes a positive lens A, whichsatisfies the following conditional expression (1), and satisfies thefollowing conditional expression (2):85.0<νdA  (1)3.90<f1/fw<11.00  (2)where νdA denotes an Abbe number at d-line (wavelength λ=587.6 nm) of amaterial of the positive lens A in the first lens group, fw denotes afocal length of the zoom lens in the wide-angle end state, and f1denotes a focal length of the first lens group.

Conditional expression (1) defines an optimum Abbe number of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variation in chromatic aberrationgenerated upon zooming from the wide-angle end state to the telephotoend state. However, conditional expression (1) has already beenexplained above, so that duplicated explanations are omitted.

Conditional expression (2) defines an appropriate range of the focallength of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (2)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the firstembodiment of the present application, at least one optical surfaceamong the first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process. With this configuration, azoom lens seen from another point of view according to the firstembodiment of the present application makes it possible to suppressghost images and flare generated by the light rays from the objectreflected from the optical surfaces, thereby realizing excellent opticalperformance.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the antireflectioncoating is a multilayer film, and the layer formed by the wet process ispreferably the outermost layer among the layers composing the multilayerfilm. With this configuration, since difference in refractive index withrespect to the air can be small, reflection of light can be small, sothat ghost images and flare can further be suppressed.

In a zoom lens seen from another point of view according to the firstembodiment of the present application, when a refractive index at d-lineof the layer formed by the wet process is denoted by nd, the refractiveindex nd is preferably 1.30 or less. With this configuration, sincedifference in refractive index with respect to the air can be small,reflection of light can be small, so that ghost images and flare canfurther be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an aperture stop. Since reflection light rays areliable to be generated on a concave surface seen from the aperture stopamong optical surfaces in the first lens group and the second lensgroup, with applying the antireflection coating on such an opticalsurface, ghost images and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the firstembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is animage side lens surface. Since the image side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the firstembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is anobject side lens surface. Since the object side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an object. Since reflection light rays are liable tobe generated on a concave surface seen from the object among opticalsurfaces in the first lens group and the second lens group, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side secondlens from the most object side lens in the first lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side second lens from the most object side lens inthe first lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidesecond lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side second lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side thirdlens from the most object side lens in the second lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side third lens from the most object side lens inthe second lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe first embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidefourth lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side fourth lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

In a zoom lens seen from another point of view according to the firstembodiment, the antireflection coating may also be formed by a dryprocess etc without being limited to the wet process. On this occasion,it is preferable that the antireflection coating contains at least onelayer of which the refractive index is equal to 1.30 or less. Thus, thesame effects as in the case of using the wet process can be obtained byforming the antireflection coating based on the dry process etc. Notethat at this time the layer of which the refractive index is equal to1.30 or less is preferably the layer of the outermost surface of thelayers composing the multi layer film.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (3) is preferablysatisfied:0.28<f1/ft<0.52  (3)where ft denotes a focal length of the zoom lens in the telephoto endstate.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (3)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (4) is preferablysatisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state. However, conditionalexpression (4) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (5) is preferablysatisfied:0.65<f1A/f1<1.75  (5)where f1A denotes a focal length of the positive lens A in the firstlens group.

Conditional expression (5) defines an optimum focal length of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming. However, conditionalexpression (5) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (6) is preferablysatisfied:1.75<φ1A/fw<4.50  (6)where φ1A denotes an effective diameter of the positive lens A in thefirst lens group.

Conditional expression (6) defines an optimum effective diameter of thepositive lens A in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming. However, conditionalexpression (6) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the first lens group preferably includes a positive lens B,which satisfies the following conditional expression (7):1.580<ndB  (7)where ndB denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of the positive lens B in the first lens group.

Conditional expression (7) defines an optimum refractive index of thematerial of the positive lens B in the first lens group, and is forrealizing high optical performance with suppressing variations inoff-axis aberrations generated upon zooming. However, conditionalexpression (7) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the first lens group preferably includes a positive lens B,which satisfies the following conditional expression (8):40.0<νdB<66.5  (8)where νdB denotes an Abbe number at d-line (wavelength λ=587.6 nm) of amaterial of the positive lens B in the first lens group.

Conditional expression (8) defines an optimum Abbe number of thematerial of the positive lens B in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming. However, conditionalexpression (8) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (9) is preferablysatisfied:0.65<f1B/f1<1.75  (9)where f1B denotes a focal length of the positive lens B in the firstlens group.

Conditional expression (9) defines an optimum focal length of thepositive lens B in the first lens group. However, conditional expression(9) has already been explained above, so that duplicated explanationsare omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the following conditional expression (10) is preferablysatisfied:1.75<φ1B/fw<4.50  (10)where φ1B denotes an effective diameter of the positive lens B in thefirst lens group.

Conditional expression (10) defines an optimum diameter of the positivelens B in the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming. However, conditionalexpression (10) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the firstembodiment, the first lens group preferably includes a negative lens,which satisfies the following conditional expressions (11) and (12):1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (11) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (12)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the firstembodiment, the first lens group is preferably composed of one negativelens and two positive lenses.

With this configuration, the thickness of the first lens group can besuppressed. Accordingly, upon zooming from the wide-angle end state tothe telephoto end state, variation in the height from the optical axisof the off-axis ray passing through the most object side surface of thefirst lens group can be suppressed, so that variations in off-axisaberrations, in particular, astigmatism can be suppressed. As a result,high optical performance can be realized.

In a zoom lens seen from another point of view according to the firstembodiment, the third lens group preferably includes a positive lens,which satisfies the following conditional expression (13):65.5<νd3 when 1.540≤nd375.0<νd3 when nd3<1.540  (13)where nd3 denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a positive lens in the third lens group, and νd3denotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the positive lens in the third lens group.

Conditional expression (13) defines an optimum Abbe number of thematerial of the positive lens in the third lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (13)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the firstembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power and a rear lens group having positive refractive power,and a distance between the front lens group and the rear lens groupdecreases upon zooming from the wide-angle end state to the telephotoend state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens seen from another point of view according to the firstembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power, a middle lens group having negative refractive power,and a rear lens group having positive refractive power, and a distancebetween the front lens group and the middle lens group varies, and adistance between the middle lens group and the rear lens group variesupon zooming from the wide-angle end state to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens seen from another point of view according to the firstembodiment, it is preferable that a distance between the front lensgroup and the middle lens group increases, and a distance between themiddle lens group and the rear lens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

Then, a zoom lens according to each Example of the first embodiment isexplained below with reference to accompanying drawings. Incidentally,detailed explanation of an antireflection coating will be explainedseparately after Example 12 of a third embodiment.

Example 1

FIG. 1 is a sectional view showing a lens configuration of a zoom lensaccording to Example 1 of a first embodiment of the present application.

As shown in FIG. 1 , the zoom lens according to Example 1 of the firstembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved at first to the image side and then to the objectside, and the third lens group G3 is moved monotonously to the objectside with respect to the image plane I such that a distance between thefirst lens group G1 and the second lens group G2 increases, and adistance between the second lens group G2 and the third lens group G3decreases. Moreover, the front lens group G31, the middle lens group G32and the rear lens group G33 are moved monotonously to the object sidewith respect to the image plane I such that a distance between the frontlens group G31 and the middle lens group G32 increases, and a distancebetween the middle lens group G32 and the rear lens group G33 decreases.Moreover, the front lens group G31 and the rear lens group G33 are movedin a body with respect to the image plane I.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a double convexpositive lens L13.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side.

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a glass mold type aspherical lens whose object side lenssurface is an aspherical surface.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

The image plane I is formed on an unillustrated imaging device. Theimaging device is constructed by a CCD, CMOS, and the like. This is thesame in the following Examples.

In the zoom lens seen from another point of view according to Example 1of the first embodiment, an antireflection coating described later isapplied to the image plane side lens surface of the negative meniscuslens L21 in the second lens group G2 and the object side lens surface ofthe double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to Example 1 ofthe first embodiment are listed in Table 1.

In (Specifications), W denotes a wide-angle end state, M denotes anintermediate focal length state, T denotes a telephoto end state, fdenotes a focal length of the zoom lens, FNO denotes an f-number, ωdenotes a half angle of view (unit: degree), Y denotes an image height,TL denotes a total lens length that is a distance from the most objectside lens surface of the first lens group G1 and the image plane I uponfocusing on infinity, and Bf denotes a back focal length.

In (Lens Data), “OP” denotes an object plane, “I” denotes an imageplane, the left most column “i” shows optical surface number, the secondcolumn “r” shows a radius of curvature of each optical surface, thethird column “d” shows a surface distance, the fourth column “nd” showsa refractive index at d-line (wavelength λ=587.6 nm), and the fifthcolumn “νd” shows an Abbe number at d-line (wavelength λ=587.6 nm). Inthe fifth column “nd” refractive index of the air nd=1.000000 isomitted. In the second column “r”, r=∞ indicates a plane surface.

An aspherical surface is expressed by the following expression when y isa height in the direction vertical to the optical axis, X(y) is adistance (sag amount) along the optical axis from a tangent plane of avertex of each aspherical surface at the height y up to each asphericalsurface, r is a radius of curvature (paraxial radius of curvature) of areference sphere, k is a conical coefficient and Cn is an n-th orderaspherical surface coefficient. Note that [E-n] represents [×10^(−n)] inthe subsequent Examples:X(y)=(y ² /r)/[1+(1−k×y ² /r ²)^(1/2)]+A4×y ⁴ +A6×y ⁶ +A8×y ⁸ +A10×y ¹⁰.

In (Aspherical Surface Data), “E-n” denotes “×10^(˜n)”, in which “n” isan integer, and for example “1.234E-05” denotes “1.234×10⁻⁵”. Eachaspherical surface is expressed in (Lens Data) by attaching “*” to theright side of the surface number.

In (Variable Distances), di (“i” a surface number) denotes a variabledistance, and Bf denotes a back focal length.

In (Lens Group Data), a start surface number “ST” of each lens group,and a focal length of each lens group are shown. In (Values forConditional Expressions), values for respective conditional expressionsare shown.

In respective tables for various values, “mm” is generally used for theunit of length such as the focal length, the radius of curvature and thedistance to the next lens surface. However, since similar opticalperformance can be obtained by an optical system proportionally enlargedor reduced its dimension, the unit is not necessarily to be limited to“mm”, and any other suitable unit can be used. The explanation ofreference symbols is the same in the other Examples including Examplesin the second and third embodiments.

TABLE 1 (Specifications) zoom ratio = 15.709 W M T f= 18.56080 104.15546291.57422 FNO= 3.60018 5.60084 5.87404 ω= 38.95554 7.45367 2.71157 Y=14.20 14.20 14.20 TL= 163.29692 225.59510 252.97281 Bf= 39.1524270.61280 82.77641 (Lens Data) i r d nd νd OP ∞ ∞  1 205.09180 2.000001.882997 40.76  2 67.52420 9.07190 1.456000 91.20  3 −361.42710 0.10000 4 70.10040 6.86700 1.603001 65.46  5 −2470.83790  (d5)  6* 84.768700.15000 1.553890 38.09  7 73.93750 1.20000 1.834807 42.72  8 17.036706.46970  9 −49.48220 1.00000 1.816000 46.62 10 52.14060 0.15000 1131.61490 5.45080 1.761820 26.56 12 −44.44820 1.19350 13 −25.135801.00000 1.816000 46.62 14 64.50360 2.42190 1.808090 22.79 15 −166.54310(d15) 16 ∞ 1.00000 Aperture Stop S 17 63.10220 3.49130 1.593190 67.87 18−50.22150 0.10000 19 58.68260 2.72200 1.487490 70.41 20 −121.434500.10000 21 48.64320 4.10420 1.487490 70.41 22 −34.50080 1.00000 1.80809022.79 23 −205.15990 (d23) 24* −66.96860 1.00000 1.693501 53.20 2526.57120 2.15810 1.761820 26.56 26 63.33840 4.78730 27 −24.70410 1.000001.729157 54.66 28 −74.86360 (d28) 29* −569.79420 3.96090 1.589130 61.1630 −23.53500 0.10000 31 37.14850 5.00600 1.487490 70.41 32 −45.196901.71640 33 −107.03630 1.00000 1.882997 40.76 34 23.36210 4.501601.548141 45.79 35 −637.55850 (Bf) I ∞ (Aspherical Surface Data) SurfaceNumber = 6 κ = 1.0000 A4 = 3.61880E−06 A6 = −6.10680E−09 A8 =−4.67380E−12 A10 = 5.77660E−14 Surface Number = 24 κ = 1.0000 A4 =3.81940E−06 A6 = −1.72450E−09 A8 = 0.00000E+00 A10 = 0.00000E+00 SurfaceNumber = 29 κ = 1.0000 A4 = −1.63630E−05 A6 = 8.94380E−09 A8 =−2.98150E−11 A10 = 2.87630E−14 (Variable Distances) W M T d5= 2.1467055.86030 80.53690 d15= 34.33830 11.46250 2.00000 d23= 3.38750 10.6693011.83690 d28= 9.44940 2.16760 1.00000 Bf= 39.15242 70.61280 82.77641(Lens Group Data) Group ST Focal Length 1 1 122.10406 2 6 −15.86654 3 1639.50539(W) 33.18380(M) 31.88175(T) 31 16 26.56694 32 24 −24.00147 33 2933.81791 (Values for Conditional Expressions)  (1) νdA = 91.20 (L12) (2) f1/fw = 6.579  (3) f1/ft = 0.419  (4) Δ1/f1 = 0.734  (5) f1A/f1 =1.029 (L12)  (6) φ1A/fw = 3.007 (φ1A = 55.81)(L12)  (7) ndB = 1.603001(L13)  (8) νdB = 65.46 (L13)  (9) f1B/f1 = 0.927 (L13) (10) φ1B/fw =2.909 (φ1B = 54.00)(L13) (11) ndN = 1.882997 (L11) (12) νdN = 40.76(L11) (13) nd3 = 1.593190 (L31) νd3 = 67.87 (L31)

FIGS. 2A, 2B and 2C are graphs showing various aberrations of the zoomlens according to Example 1 of the first embodiment upon focusing on aninfinitely distant object, in which FIG. 2A is a wide-angle end state,FIG. 2B is an intermediate focal length state, and FIG. 2C is atelephoto end state.

In respective graphs, FNO denotes an f-number, A denotes a half angle ofview (unit: degree), d denotes an aberration curve at d-line (wavelengthλ=587.6 nm), and g denotes an aberration curve at g-line (wavelengthλ=435.8 nm). Aberration curve with out specified is an aberration curvewith respect to d-line. In graphs showing astigmatism, a solid lineindicates a sagittal image plane, and a broken line indicates ameridional image plane. The explanations of reference symbols are thesame in the other Examples including Examples in the second and thirdembodiments.

As is apparent from various graphs, the zoom lens according to Example 1of the first embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

FIG. 3 is a sectional view showing the lens configuration of the lenssystem according to Example 1 of the first embodiment and is anexplanatory view, in which light rays reflected from afirst-ghost-generating surface are reflected by asecond-ghost-generating surface.

As shown in FIG. 3 , when light rays BM from an object are incident onthe zoom lens, the rays are reflected by the object side lens surface (afirst-ghost-generating surface whose surface number is 9) of the doubleconcave negative lens L22, and the reflected light rays are reflectedagain by the image plane I side lens surface (a second-ghost-generatingsurface whose surface number is 8) of the negative meniscus lens L21 toreach the image plane I with generating ghost images. Incidentally, thefirst-ghost-generating surface 9 is a concave surface seen from theobject side, and the second-ghost-generating surface 8 is a concavesurface seen from the aperture stop S. With forming an antireflectioncoating corresponding to a broad wavelength range to such lens surfaces,it becomes possible to effectively suppress ghost images and flare.

Example 2

FIG. 4 is a sectional view showing a lens configuration of a zoom lensaccording to Example 2 of the first embodiment of the presentapplication.

As shown in FIG. 4 , the zoom lens according to Example 2 of the firstembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, and a rear lens group G32having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved monotonously to the object side, and the thirdlens group G3 is moved monotonously to the object side with respect tothe image plane I such that a distance between the first lens group G1and the second lens group G2 increases, and a distance between thesecond lens group G2 and the third lens group G3 decreases. Moreover,the front lens group G31, and the rear lens group G32 are movedmonotonously to the object side with respect to the image plane I suchthat a distance between the front lens group G31 and the rear lens groupG32 decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a double concave negative lens L24.The negative meniscus lens L21 disposed to the most object side of thesecond lens group G2 is a compound type aspherical lens whose objectside lens surface is formed as an aspherical surface by applying a resinlayer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a cementedlens constructed by a double convex positive lens L32 cemented with anegative meniscus lens L33 having a concave surface facing the objectside, and a cemented lens constructed by a double concave negative lensL34 cemented with a positive meniscus lens L35 having a convex surfacefacing the object side. The double concave negative lens L34 is acompound type aspherical lens whose object side lens surface is formedas an aspherical surface by applying a resin layer.

The rear lens group G32 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L41, a cementedlens constructed by a double convex positive lens L42 cemented with adouble concave negative lens L43, and a double convex positive lens L44.The double convex positive lens L41 disposed to the most object side ofthe rear lens group G32 is a glass mold type aspherical lens whoseobject side lens surface is an aspherical surface. Light rays come outfrom the double convex positive lens L44 form an image on the imageplane I.

In the zoom lens seen from another point of view according to Example 2of the first embodiment, an antireflection coating described later isapplied to the object side lens surface of the positive meniscus lensL13 in the first lens group G1 and the image side lens surface of thedouble convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to Example 2 ofthe first embodiment are listed in Table 2.

TABLE 2 (Specifications) zoom ratio = 15.666 W M T f= 18.57581 134.79308291.01598 FNO= 3.58467 6.30198 6.35739 ω= 38.75301 5.90773 2.74550 Y=14.20 14.20 14.20 TL= 141.06118 214.13726 227.18745 Bf= 38.0232885.33826 92.60805 (Lens Data) i r d nd νd OP ∞ ∞  1 107.02060 1.800001.903658 31.31  2 61.29680 9.01320 1.456500 90.27  3 −505.77970 0.10000 4 56.57080 6.56600 1.603001 65.44  5 263.14480  (d5)  6* 107.663300.15000 1.553890 38.09  7 79.43570 1.20000 1.816000 4 6.62  8 12.549805.89610  9 −28.13610 1.00000 1.816000 46.62 10 76.81030 0.10000 1129.03300 5.08050 1.846660 23.78 12 −28.29410 0.70210 13 −20.323401.00000 1.788001 47.37 14 328.32220 (d14) 15 ∞ 0.50000 Aperture Stop S16 38.51440 4.38040 1.527510 66.72 17 −31.08680 0.10000 18 24.827805.70920 1.497000 81.64 19 −22.48490 1.00000 1.850260 32.35 20−1199.41670 3.00000 21* −52.55750 0.10000 1.553890 38.09 22 −56.776901.00000 1.772499 49.60 23 32.93540 1.94820 1.805181 25.42 24 83.42590(d24) 25* 38.17010 5.15170 1.677900 54.89 26 −30.30750 0.10000 27119.12160 5.79370 1.511790 49.72 28 −16.92620 1.00000 1.878780 41.73 2940.26250 0.79940 30 88.76870 4.01880 1.497970 53.26 31 −31.87250 (Bf) I∞ (Aspherical Surface Data) Surface Number = 6 κ = 1.0000 A4 =8.23600E−06 A6 = 2.68070E−08 A8 = −2.85680E−10 A10 = 8.96110E−13 SurfaceNumber = 21 κ = 1.0000 A4 = 8.39680E−06 A6 = 4.90050E−09 A8 =0.00000E+00 A10 = 0.00000E+00 Surface Number = 25 κ = 1.0000 A4 =−1.05940E−05 A6 = 2.60370E−08 A8 = 0.00000E+00 A10 = 0.00000E+00(Variable Distances) W M T d5= 2.12080 50.67230 62.67010 d14= 23.691307.80730 1.80000 d24= 10.01650 3.11010 2.90000 Bf= 38.02328 85.3382692.60805 (Lens Group Data) Group ST Focal Length 1 1 95.68946 2 6−11.46195 3 15 31.13029(W) 27.66506(M) 27.57169(T) 31 15 42.77504 32 2540.12768 (Values for Conditional Expressions)  (1) νdA = 90.27 (L12) (2) f1/fw = 5.151  (3) f1/ft = 0.329  (4) Δ1/f1 = 0.900  (5) f1A/f1 =1.258 (L12)  (6) φ1A/fw = 2.998 (φ1A = 55.69)(L12)  (7) ndB = 1.603001(L13)  (8) νdB = 65.44 (L13)  (9) f1B/f1 = 1.234 (L13) (10) φ1B/fw =2.799 (φ1B = 52.00)(L13) (11) ndN = 1.903658 (L11) (12) νdN = 31.31(L11) (13) nd3 = 1.497000 (L32) νd3 = 81.64 (L32)

FIGS. 5A, 5B and 50 are graphs showing various aberrations of the zoomlens according to Example 2 of the first embodiment upon focusing on aninfinitely distant object, in which FIG. 5A is a wide-angle end state,FIG. 5B is an intermediate focal length state, and FIG. 50 is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 2of the first embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Example 3

FIG. 6 is a sectional view showing a lens configuration of a zoom lensaccording to Example 3 of a first embodiment of the present application.

As shown in FIG. 6 , the zoom lens according to Example 3 of the firstembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a double convexpositive lens L13.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side.

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a glass mold type aspherical lens whose object side lenssurface is an aspherical surface.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 3of the first embodiment, an antireflection coating described later isapplied to the image side lens surface of the double convex positivelens L12 in the first lens group G1 and the object side lens surface ofthe double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to Example 3 ofthe first embodiment are listed in Table 3.

TABLE 3 (Specifications) zoom ratio = 15.714 W M T f= 18.55566 103.95947291.57591 FNO= 3.63338 5.62730 5.88308 ω= 38.94112 7.46798 2.71133 Y=14.20 14.20 14.20 TL= 163.38092 225.17861 252.25324 Bf= 39.1716270.49651 82.47674 (Lens Data) i r d nd νd OP ∞ ∞  1 193.38060 2.000001.883000 40.77  2 66.83560 9.23080 1.437000 95.00  3 −341.14920 0.10000 4 68.78950 6.98760 1.603000 65.47  5 −2649.89320  (d5)  6* 84.768700.15000 1.553890 38.09  7 73.93750 1.20000 1.834810 42.72  8 16.948206.42970  9 −53.17850 1.00000 1.816000 46.63 10 46.70940 0.15000 1130.63920 5.37880 1.761820 26.56 12 −48.96880 1.39690 13 −24.422501.00000 1.816000 46.63 14 69.10450 2.52380 1.808090 22.79 15 −121.94360(d15) 16 ∞ 1.00000 Aperture Stop S 17 66.08180 3.43590 1.592820 68.69 18−50.37120 0.10000 19 59.42650 2.78060 1.487490 70.45 20 −108.478700.10000 21 49.67940 4.11660 1.487490 70.45 22 −33.83640 1.00000 1.80809022.79 23 −167.67900 (d23) 24* −64.89240 1.00000 1.693500 53.22 2527.12400 2.14440 1.761820 26.56 26 65.84410 4.73170 27 −25.14850 1.000001.729160 54.66 28 −73.72860 (d28) 29* −448.31420 3.90050 1.589130 61.1830 −23.64180 0.10000 31 37.43750 4.98090 1.487490 70.45 32 −44.964101.73250 33 −102.62990 1.00000 1.883000 40.77 34 23.17730 4.511701.548140 45.79 35 −619.02620 (Bf) I ∞ (Aspherical Surface Data) SurfaceNumber = 6 κ = 1.0000 A4 = 4.16398E−06 A6 = −7.55222E−09 A8 =−2.91689E−12 A10 = 5.62106E−14 Surface Number = 24 κ = 1.0000 A4 =3.83569E−06 A6 = −1.03578E−09 A8 = 0.00000E+00 A10 = 0.00000E+00 SurfaceNumber = 29 κ = 1.0000 A4 = −1.60868E−05 A6 = 8.16360E−09 A8 =−3.55020E−11 A10 = 7.60058E−14 (Variable Distances) W M T d5= 2.1270055.32280 79.77200 d15= 34.07780 11.35470 2.00000 d23= 3.36200 10.6767011.82210 d28 = 9.46010 2.14550 1.00000 Bf= 39.17162 70.49651 82.47674(Lens Group Data) Group ST Focal Length 1 1 120.77885 2 6 −15.59572 3 1639.12629(W) 32.72813(M) 31.47773(T) 31 16 26.38558 32 24 −24.49396 33 2934.76717 (Values for Conditional Expressions)  (1) νdA = 95.00 (L12) (2) f1/fw = 6.509  (3) f1/ft = 0.414  (4) Δ1/f1 = 0.736  (5) f1A/f1 =1.066 (L12)  (6) φ1A/fw = 3.043 (φ1A = 56.47)(L12)  (7) ndB = 1.603000(L13)  (8) νdB = 65.47 (L13)  (9) f1B/f1 = 0.922 (L13) (10) φ1B/fw =2.910 (φ1B = 54.00)(L13) (11) ndN = 1.883000 (L11) (12) νdN = 40.77(L11) (13) nd3 = 1.592820 (L31) νd3 = 68.69 (L31)

FIGS. 7A, 7B and 7C are graphs showing various aberrations of the zoomlens according to Example 3 of the first embodiment upon focusing on aninfinitely distant object, in which FIG. 7A is a wide-angle end state,FIG. 7B is an intermediate focal length state, and FIG. 7C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 3of the first embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Then, an outline of a method for manufacturing a zoom lens according tothe first embodiment is explained.

FIG. 24 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the first embodiment.

The method for manufacturing a zoom lens according to the firstembodiment is a method for manufacturing a zoom lens including, in orderfrom an object side along an optical axis, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, and a third lens group having positive refractivepower, and being constructed such that at least one optical surface inthe first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process, the method including stepsS11 through S13.

Step S11: disposing the first lens group, the second lens group and thethird lens group movably such that upon zooming from a wide-angle endstate to a telephoto end state, a distance between the first lens groupand the second lens group increases, and a distance between the secondlens group and the third lens group decreases.

Step S12: disposing a positive lens A satisfying the followingconditional expression (1) into the first lens group:85.0<νdA  (1)where νdA denotes an Abbe number at d-line (wavelength λ=587.6 nm) ofthe positive lens A in the first lens group.

Step S13: disposing each lens with satisfying conditional expression(2):3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

With this method for manufacturing a zoom lens according to the firstembodiment, it becomes possible to manufacture a zoom lens havingexcellent optical performance with suppressing variations in aberrationsand ghost images and flare.

Second Embodiment

A zoom lens according to a second embodiment of the present applicationis explained below.

A zoom lens according to the second embodiment of the presentapplication includes, in order from an object side along an opticalaxis, a first lens group having positive refractive power, a second lensgroup having negative refractive power, and a third lens group havingpositive refractive power. Upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increases, and a distance between the second lensgroup and the third lens group decreases. With this configuration, itbecomes possible to realize a zoom lens, and, at the same time, suppressvariation in distortion generated upon zooming.

A zoom lens according to the second embodiment includes a positive lensA′ that satisfies the following conditional expressions (14) and (15),and satisfies the following conditional expression (2):1.540<ndA′  (14)66.5<νdA′  (15)3.90<f1/fw<11.00  (2)where ndA′ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of the positive lens A′, νdA′ denotes an Abbe number atd-line (wavelength λ=587.6 nm) of a material of the positive lens A′, fwdenotes a focal length of the zoom lens in the wide-angle end state, andf1 denotes a focal length of the first lens group.

Conditional expression (14) defines an optimum refractive index of thematerial of the positive lens A′, and is for realizing high opticalperformance with suppressing variations in spherical aberration andcurvature of field generated upon zooming from the wide-angle end stateto the telephoto end state.

When the value ndA′ is equal to or falls below the lower limit ofconditional expression (14), it becomes difficult to suppress variationsin spherical aberration and curvature of field, so that high opticalperformance cannot be realized.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (14) to 1.550.

Conditional expression (15) defines an optimum Abbe number of thematerial of the positive lens A′, and is for realizing high opticalperformance with suppressing variation in chromatic aberration generatedupon zooming from the wide-angle end state to the telephoto end state.

When the value νdA′ is equal to or falls below the lower limit ofconditional expression (15), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (15) to 67.5.

Conditional expression (2) defines an appropriate range of the focallength of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (2)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens according to the second embodiment, the followingconditional expression (3) is preferably satisfied:0.28<f1/ft<0.52  (3)where ft denotes a focal length of the zoom lens in the telephoto endstate.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (3)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens according to the second embodiment, the followingconditional expression (4) is preferably satisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state. However, conditionalexpression (4) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens according to the second embodiment, the third lens grouppreferably includes a positive lens A′.

With this configuration, it becomes possible to suppress variations inlongitudinal chromatic aberration and spherical aberration generatedupon zooming from the wide-angle end state to the telephoto end state,so that high optical performance can be realized.

In a zoom lens according to the second embodiment, the followingconditional expression (16) is preferably satisfied:0.75<f3A′/f3<2.25  (16)where f3 denotes a focal length of the third lens group, and f3A′denoted a focal length of the positive lens A′ in the third lens group.

Conditional expression (16) defines an optimum focal length of thepositive lens A′ in the third lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand on-axis aberrations generated upon zooming.

When the ratio f3A′/f3 is equal to or falls below the lower limit ofconditional expression (16), refractive power of the positive lens A′becomes strong, so that upon zooming from the wide-angle end state tothe telephoto end state, variation in refractive power in accordancewith variation in the height from the optical axis of the on axis raypassing through the positive lens A′ becomes large. As a result, itbecomes difficult to suppress variations in longitudinal chromaticaberration and spherical aberration, so that high optical performancecannot be realized.

On the other hand, when the ratio f3A′/f3 is equal to or exceeds theupper limit of conditional expression (16), refractive power of thepositive lens A′ becomes small, so that refractive power of the positivelens other than the positive lens A′ in the third lens group becomesstrong. As a result, upon zooming from the wide-angle end state to thetelephoto end state, variation in refractive power in accordance withvariation in the height from the optical axis of the off-axis raypassing through the positive lens A′ becomes large, so that it becomesdifficult to suppress variations in longitudinal chromatic aberrationand spherical aberration. Accordingly, high optical performance cannotbe realized.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (16) to 0.90.

In order to secure the effect of the second embodiment, it is preferableto set the upper limit of conditional expression (16) to 1.95.

In a zoom lens according to the second embodiment, the first lens grouppreferably includes the positive lens A′.

With this configuration, it becomes possible to suppress variations inlongitudinal chromatic aberration generated upon zooming from thewide-angle end state to the telephoto end state, so that high opticalperformance can be realized.

In a zoom lens according to the second embodiment, the followingconditional expression (17) is preferably satisfied:0.65<f1A′/f1<1.75  (17)where f1A′ denotes a focal length of the positive lens A′ in the firstlens group.

Conditional expression (17) defines an optimum focal length of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming.

When the ratio f1A′/f1 is equal to or falls below the lower limit ofconditional expression (17), refractive power of the positive lens A′becomes strong, variation in refractive power in accordance withvariation in the height from the optical axis of the off-axis ray uponzooming from the wide-angle end state to the telephoto end state becomeslarge. As a result, it becomes difficult to suppress variations inlateral chromatic aberration and off-axis aberrations, in particular,astigmatism, so that high optical performance cannot be realized.

On the other hand, when the ratio f1A′/f1 is equal to or exceeds theupper limit of conditional expression (17), refractive power of thepositive lens A′ becomes weak, so that refractive power of the positivelens other the positive lens A′ in the first lens group becomes strong.As a result, upon zooming from the wide-angle end state to the telephotoend state, variation in refractive power in accordance with variation inthe height from the optical axis of the off-axis ray passing through thepositive lens A′ becomes large, so that it becomes difficult to suppressvariations in lateral chromatic aberration and off-axis aberrations, inparticular, astigmatism. Accordingly, high optical performance cannot berealized.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (17) to 0.80.

In order to secure the effect of the second embodiment, it is preferableto set the upper limit of conditional expression (17) to 1.35.

In a zoom lens according to the second embodiment, the followingconditional expression (18) is preferably satisfied:1.75<φ1A′/fw<4.50  (18)where φ1A′ denotes an effective diameter of the positive lens A′ in thefirst lens group.

Conditional expression (18) defines an optimum effective diameter of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming.

When the ratio φ1A′/fw is equal to or falls below the lower limit ofconditional expression (18), upon zooming from the wide-angle end stateto the telephoto end state, variation in the height from the opticalaxis of the off-axis ray passing through the positive lens A′ in thefirst lens group becomes small, so that it becomes difficult to suppressvariations in off-axis aberrations, in particular, astigmatism. As aresult, high optical performance cannot be realized.

On the other hand, when the ratio φ1A′/fw is equal to or exceeds theupper limit of conditional expression (18), upon zooming from thewide-angle end state to the telephoto end state, variation in the heightfrom the optical axis of the off-axis ray passing through the positivelens A′ in the first lens group becomes large, so that it becomesdifficult to suppress variations in lateral chromatic aberration andoff-axis aberrations, in particular, astigmatism. As a result, highoptical performance cannot be realized.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (18) to 2.45.

In order to secure the effect of the second embodiment, it is preferableto set the upper limit of conditional expression (18) to 3.80.

In a zoom lens according to the second embodiment, the followingconditional expression (19) is preferably satisfied:0.055<φ1A′/ft<0.420  (19)where ft denotes a focal length of the zoom lens in the telephoto endstate, and φ1A′ denotes an effective diameter of the positive lens A′ inthe first lens group.

Conditional expression (19) defines an optimum effective diameter of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming.

When the ratio φ1A′/ft is equal to or falls below the lower limit ofconditional expression (19), upon zooming from the wide-angle end stateto the telephoto end state, variation in the height from the opticalaxis of the off-axis ray passing through the positive lens A′ in thefirst lens group becomes small, so that it becomes difficult to suppressvariations in off-axis aberrations, in particular, astigmatism. As aresult, high optical performance cannot be realized.

On the other hand, when the ratio φ1A′/ft is equal to or exceeds theupper limit of conditional expression (19), upon zooming from thewide-angle end state to the telephoto end state, variation in the heightfrom the optical axis of the off-axis ray passing through the positivelens A′ in the first lens group becomes large, so that it becomesdifficult to suppress variations in lateral chromatic aberration andoff-axis aberrations, in particular, astigmatism. As a result, highoptical performance cannot be realized.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (19) to 0.080.

In order to secure the effect of the second embodiment, it is preferableto set the upper limit of conditional expression (19) to 0.350.

In a zoom lens according to the second embodiment, the first lens grouppreferably includes two positive lenses.

With this configuration, the thickness of the first lens group can besuppressed, so that upon zooming from the wide-angle end state to thetelephoto end state, variation in the height from the optical axis ofthe off-axis ray passing through the most object side lens surface ofthe first lens group can be suppressed. As a result, variations inoff-axis aberrations, in particular, astigmatism can be suppressed, sothat high optical performance can be realized.

In a zoom lens according to the second embodiment, the followingconditional expressions (11) and (12) are preferably satisfied:1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (11) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (12)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens according to the second embodiment, the first lens grouppreferably has only one negative lens.

With this configuration, the thickness of the first lens group can besuppressed, so that upon zooming from the wide-angle end state to thetelephoto end state, variation in the height from the optical axis ofthe off-axis ray passing through the most object side lens surface ofthe first lens group can be suppressed. As a result, variations inoff-axis aberrations, in particular, astigmatism can be suppressed, sothat high optical performance can be realized.

In a zoom lens according to the second embodiment, the followingconditional expression (20) is preferably satisfied:75.0<νdB′  (20)where νdB′ denotes an Abbe number at d-line (wavelength λ=587.6 nm) of amaterial of the positive lens B′ in the first lens group.

Conditional expression (20) defines an optimum Abbe number of thematerial of the positive lens B′, and is for realizing high opticalperformance with suppressing variation in chromatic aberration generatedupon zooming from the wide-angle end state to the telephoto end state.

When the value νdB′ is equal to or falls below the lower limit ofconditional expression (20), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

In a zoom lens according to the second embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power and a rear lens group havingpositive refractive power, and a distance between the front lens groupand the rear lens group decreases upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens according to the second embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power, a middle lens group havingnegative refractive power, and a rear lens group having positiverefractive power, and a distance between the front lens group and themiddle lens group varies, and a distance between the middle lens groupand the rear lens group varies upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens according to the second embodiment, it is preferable thata distance between the front lens group and the middle lens groupincreases, and a distance between the middle lens group and the rearlens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

In a zoom lens according to the second embodiment, the front lens grouppreferably includes a positive lens A′.

With this configuration, it becomes possible to suppress variations inlongitudinal chromatic aberration and spherical aberration generatedupon zooming from the wide-angle end state to the telephoto end state,so that high optical performance can be realized.

In a zoom lens according to the second embodiment, the followingconditional expression (21) is preferably satisfied:0.55<f31A′/f31<2.45  (21)where f31 denotes a focal length of the front lens group, and f31A′denotes a focal length of the positive lens A′ in the front lens group.

Conditional expression (21) defines an optimum focal length of thepositive lens A′ in the front lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand on-axis aberrations generated upon zooming.

When the ratio f31A′/f31 is equal to or falls below the lower limit ofconditional expression (21), refractive power of the positive lens A′becomes strong, so that upon zooming from the wide-angle end state tothe telephoto end state, variation in refractive power in accordancewith variation in the height of the on-axis ray passing through thepositive lens A′ becomes large. As a result, it becomes difficult tosuppress variations in longitudinal chromatic aberration and sphericalaberration, so that high optical performance cannot be obtained.

On the other hand, when the ratio f31A′/f31 is equal to or exceeds theupper limit of conditional expression (21), refractive power of thepositive lens A′ becomes weak, positive refractive power other than thepositive lens A′ in the front lens group becomes strong, so that uponzooming from the wide-angle end state to the telephoto end state,variation in refractive power in accordance with variation in the heightof the off-axis ray passing through the positive lens A′ becomes large.As a result, it becomes difficult to suppress variations in longitudinalchromatic aberration and spherical aberration, so that high opticalperformance cannot be obtained.

In order to secure the effect of the second embodiment, it is preferableto set the lower limit of conditional expression (21) to 0.73.

In order to secure the effect of the second embodiment, it is preferableto set the upper limit of conditional expression (21) to 1.95.

Then, a zoom lens seen from another point of view according to thesecond embodiment of the present application includes, in order from anobject side along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power. Upon zoomingfrom a wide-angle end state to a telephoto end state, a distance betweenthe first lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases. Withthis configuration, it becomes possible to realize a zoom lens, and, atthe same time, suppress variation in distortion generated upon zooming.

A zoom lens seen from another point of view according to the secondembodiment includes a positive lens A′ that satisfies the followingconditional expressions (14) and (15), and satisfies the followingconditional expression (2):1.540<ndA′  (14)66.5<νdA′  (15)3.90<f1/fw<11.00  (2)where ndA′ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of the positive lens A′, νdA′ denotes an Abbe number atd-line (wavelength λ=587.6 nm) of a material of the positive lens A′, fwdenotes a focal length of the zoom lens in the wide-angle end state, andf1 denotes a focal length of the first lens group.

Conditional expression (14) defines an optimum refractive index of thematerial of the positive lens A′, and is for realizing high opticalperformance with suppressing variations in spherical aberration andcurvature of field generated upon zooming from the wide-angle end stateto the telephoto end state. However, conditional expression (14) hasalready been explained, so that duplicated explanations are omitted.

Conditional expression (15) defines an optimum Abbe number of thematerial of the positive lens A′, and is for realizing high opticalperformance with suppressing variation in chromatic aberration generatedupon zooming from the wide-angle end state to the telephoto end state.However, conditional expression (15) has already been explained, so thatduplicated explanations are omitted.

Conditional expression (2) defines an appropriate range of the focallength of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (2)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the secondembodiment of the present application, at least one optical surfaceamong the first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process. With this configuration, azoom lens seen from another point of view according to the secondembodiment of the present application makes it possible to suppressghost images and flare generated by the light rays from the objectreflected from the optical surfaces, thereby realizing excellent opticalperformance.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the antireflectioncoating is a multilayer film, and the layer formed by the wet process ispreferably the outermost layer among the layers composing the multilayerfilm. With this configuration, since difference in refractive index withrespect to the air can be small, reflection of light can be small, sothat ghost images and flare can further be suppressed.

In a zoom lens seen from another point of view according to the secondembodiment of the present application, when a refractive index at d-lineof the layer formed by the wet process is denoted by nd, the refractiveindex nd is preferably 1.30 or less. With this configuration, sincedifference in refractive index with respect to the air can be small,reflection of light can be small, so that ghost images and flare canfurther be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an aperture stop. Since reflection light rays areliable to be generated on a concave surface seen from the aperture stopamong optical surfaces in the first lens group and the second lensgroup, with applying the antireflection coating on such an opticalsurface, ghost images and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the secondembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is animage side lens surface. Since the image side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the secondembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is anobject side lens surface. Since the object side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an object side. Since reflection light rays are liableto be generated on a concave surface seen from the object among opticalsurfaces in the first lens group and the second lens group, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side secondlens from the most object side lens in the first lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side second lens from the most object side lens inthe first lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidesecond lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side second lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side thirdlens from the most object side lens in the second lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side third lens from the most object side lens inthe second lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe second embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidefourth lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side fourth lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

In a zoom lens seen from another point of view according to the secondembodiment, the antireflection coating may also be formed by a dryprocess etc without being limited to the wet process. On this occasion,it is preferable that the antireflection coating contains at least onelayer of which the refractive index is equal to 1.30 or less. Thus, thesame effects as in the case of using the wet process can be obtained byforming the antireflection coating based on the dry process etc. Notethat at this time the layer of which the refractive index is equal to1.30 or less is preferably the layer of the outermost surface of thelayers composing the multi layer film.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (3) is preferablysatisfied:0.28<f1/ft<0.52  (3)where ft denotes a focal length of the zoom lens in the telephoto endstate.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (3)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (4) is preferablysatisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state. However, conditionalexpression (4) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, the third lens group preferably includes a positive lens A′.

With this configuration, it becomes possible to suppress variations inlongitudinal chromatic aberration and spherical aberration generatedupon zooming from the wide-angle end state to the telephoto end state,so that high optical performance can be realized.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (16) is preferablysatisfied:0.75<f3A′/f3<2.25  (16)where f3 denotes a focal length of the third lens group, and f3A′denotes a focal length of the positive lens A′ in the third lens group.

Conditional expression (16) defines an optimum focal length of thepositive lens A′ in the third lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand on-axis aberrations generated upon zooming. However, conditionalexpression (16) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, the first lens group preferably includes the positive lensA′.

With this configuration, it becomes possible to suppress variations inlongitudinal chromatic aberration generated upon zooming from thewide-angle end state to the telephoto end state, so that high opticalperformance can be realized.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (17) is preferablysatisfied:0.65<f1A′/f1<1.75  (17)where f1A′ denotes a focal length of the positive lens A′ in the firstlens group.

Conditional expression (17) defines an optimum focal length of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming. However, conditionalexpression (17) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (18) is preferablysatisfied:1.75<φ1A′/fw<4.50  (18)where φ1A′ denotes an effective diameter of the positive lens A′ in thefirst lens group.

Conditional expression (18) defines an optimum effective diameter of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming. However, conditionalexpression (18) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (19) is preferablysatisfied:0.055<φ1A′/ft<0.420  (19)where ft denotes a focal length of the zoom lens in the telephoto endstate, and φ1A′ denotes an effective diameter of the positive lens A′ inthe first lens group.

Conditional expression (19) defines an optimum effective diameter of thepositive lens A′ in the first lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand off-axis aberrations generated upon zooming. However, conditionalexpression (19) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, the first lens group preferably includes two positivelenses.

With this configuration, the thickness of the first lens group can besuppressed, so that upon zooming from the wide-angle end state to thetelephoto end state, variation in the height from the optical axis ofthe off-axis ray passing through the most object side lens surface ofthe first lens group can be suppressed. As a result, variations inoff-axis aberrations, in particular, astigmatism can be suppressed, sothat high optical performance can be realized.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expressions (11) and (12) arepreferably satisfied:1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (11) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (12)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the secondembodiment, the first lens group preferably has only one negative lens.

With this configuration, the thickness of the first lens group can besuppressed, so that upon zooming from the wide-angle end state to thetelephoto end state, variation in the height from the optical axis ofthe off-axis ray passing through the most object side lens surface ofthe first lens group can be suppressed. As a result, variations inoff-axis aberrations, in particular, astigmatism can be suppressed, sothat high optical performance can be realized.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (20) is preferablysatisfied:75.0<νdB′  (20)where νdB′ denotes an Abbe number at d-line (wavelength λ=587.6 nm) of amaterial of the positive lens B′ in the first lens group.

Conditional expression (20) defines an optimum Abbe number of thematerial of the positive lens B′, and is for realizing high opticalperformance with suppressing variation in chromatic aberration generatedupon zooming from the wide-angle end state to the telephoto end state.However, conditional expression (20) has already been explained above,so that duplicated explanations are omitted.

In a zoom lens seen from another point of view according to the secondembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power and a rear lens group having positive refractive power,and a distance between the front lens group and the rear lens groupdecreases upon zooming from the wide-angle end state to the telephotoend state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens seen from another point of view according to the secondembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power, a middle lens group having negative refractive power,and a rear lens group having positive refractive power, and a distancebetween the front lens group and the middle lens group varies, and adistance between the middle lens group and the rear lens group variesupon zooming from the wide-angle end state to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens seen from another point of view according to the secondembodiment, it is preferable that a distance between the front lensgroup and the middle lens group increases, and a distance between themiddle lens group and the rear lens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

In a zoom lens seen from another point of view according to the secondembodiment, the following conditional expression (21) is preferablysatisfied:0.55<f31A′/f31<2.45  (21)where f31 denotes a focal length of the front lens group, and f31A′denotes a focal length of the positive lens A′ in the front lens group.

Conditional expression (21) defines an optimum focal length of thepositive lens A′ in the front lens group, and is for realizing highoptical performance with suppressing variations in chromatic aberrationand on-axis aberrations generated upon zooming. However, conditionalexpression (21) has already been explained above, so that duplicatedexplanations are omitted.

Then, a zoom lens according to each Example of the second embodiment isexplained below with reference to accompanying drawings. Incidentally,detailed explanation of an antireflection coating will be explainedseparately after Example 12 of a third embodiment.

Example 4

FIG. 1 is a sectional view showing a lens configuration of a zoom lensaccording to Example 4 of the second embodiment of the presentapplication.

As shown in FIG. 1 , the zoom lens according to Example 4 of the secondembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved at first to the image side and then to the objectside, and the third lens group G3 is moved monotonously to the objectside with respect to the image plane I such that a distance between thefirst lens group G1 and the second lens group G2 increases, and adistance between the second lens group G2 and the third lens group G3decreases. Moreover, the front lens group G31, the middle lens group G32and the rear lens group G33 are moved monotonously to the object sidewith respect to the image plane I such that a distance between the frontlens group G31 and the middle lens group G32 increases, and a distancebetween the middle lens group G32 and the rear lens group G33 decreases.Moreover, the front lens group G31 and the rear lens group G33 are movedin a body with respect to the image plane I.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a double convexpositive lens L13.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side. The double convexpositive lens L31 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a glass mold type aspherical lens whose object side lenssurface is an aspherical surface.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 4of the second embodiment, an antireflection coating described later isapplied to the image plane side lens surface of the negative meniscuslens L21 in the second lens group G2 and the object side lens surface ofthe double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to Example 4 ofthe second embodiment are listed in Table 4.

TABLE 4 (Specifications) zoom ratio = 15.709 W M T f= 18.56080 104.15546291.57422 FNO= 3.60018 5.60084 5.87404 ω= 38.95554 7.45367 2.71157 Y=14.20 14.20 14.20 TL= 163.29692 225.59510 252.97281 Bf= 39.1524270.61280 82.77641 (Lens Data) i r d nd νd OP ∞ ∞  1 205.09180 2.000001.882997 40.76  2 67.52420 9.07190 1.456000 91.20  3 −361.42710 0.10000 4 70.10040 6.86700 1.603001 65.46  5 −2470.83790  (d5)  6* 84.768700.15000 1.553890 38.09  7 73.93750 1.20000 1.834807 42.72  8 17.036706.46970  9 −49.48220 1.00000 1.816000 46.62 10 52.14060 0.15000 1131.61490 5.45080 1.761820 26.56 12 −44.44820 1.19350 13 −25.135801.00000 1.816000 46.62 14 64.50360 2.42190 1.808090 22.79 15 −166.54310(d15) 16 ∞ 1.00000 Aperture Stop S 17 63.10220 3.49130 1.593190 67.87 18−50.22150 0.10000 19 58.68260 2.72200 1.487490 70.41 20 −121.434500.10000 21 48.64320 4.10420 1.487490 70.41 22 −34.50080 1.00000 1.80809022.79 23 −205.15990 (d23) 24* −66.96860 1.00000 1.693501 53.20 2526.57120 2.15810 1.761820 26.56 26 63.33840 4.78730 27 −24.70410 1.000001.729157 54.66 28 −74.86360 (d28) 29* −569.79420 3.96090 1.589130 61.1630 −23.53500 0.10000 31 37.14850 5.00600 1.487490 70.41 32 −45.196901.71640 33 −107.03630 1.00000 1.882997 40.76 34 23.36210 4.501601.548141 45.79 35 −637.55850 (Bf) I ∞ (Aspherical Surface Data) SurfaceNumber = 6 κ = 1.0000 A4 = 3.61880E−06 A6 = −6.10680E−09 A8 =−4.67380E−12 A10 = 5.77660E−14 Surface Number = 24 κ = 1.0000 A4 =3.81940E−06 A6 = −1.72450E−09 A8 = 0.00000E+00 A10 = 0.00000E+00 SurfaceNumber = 29 κ = 1.0000 A4 = −1.63630E−05 A6 = 8.94380E−09 A8 =−2.98150E−11 A10 = 2.87630E−14 (Variable Distances) W M T d5= 2.1467055.86030 80.53690 d15= 34.33830 11.46250 2.00000 d23= 3.38750 10.6693011.83690 d28= 9.44940 2.16760 1.00000 Bf= 39.15242 70.61280 82.77641(Lens Group Data) Group ST Focal Length 1 1 122.10406 2 6 −15.86654 3 1639.50539(W) 33.18380(M) 31.88175(T) 31 16 26.56694 32 24 −24.00147 33 2933.81791 (Values for Conditional Expressions)  (2) f1/fw = 6.579  (3)f1/ft = 0.419  (4) Δ1/f1 = 0.734 (11) ndN = 1.882997 (L11) (12) νdN =40.76 (L11) (14) ndA′ = 1.593190 (L31) (15) νdA′ = 67.87 (L31) (16)f3A′/f3 = 1.207 (L31)(W) (16) f3A′/f3 = 1.437 (L31)(M) (16) f3A′/f3 =1.496 (L31)(T) (20) νdB′ = 91.20 (L12) (21) f31A′/f31 = 1.795 (L31)

FIGS. 2A, 2B and 2C are graphs showing various aberrations of the zoomlens according to Example 4 of the second embodiment upon focusing on aninfinitely distant object, in which FIG. 2A is a wide-angle end state,FIG. 2B is an intermediate focal length state, and FIG. 2C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 4of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

FIG. 3 is a sectional view showing the lens configuration of the lenssystem seen from another point of view according to Example 4 of thesecond embodiment and is an explanatory view, in which light raysreflected from a first-ghost-generating surface are reflected by asecond-ghost-generating surface. As shown in FIG. 3 , when light rays BMfrom an object are incident on the zoom lens, the rays are reflected bythe object side lens surface (a first-ghost-generating surface whosesurface number is 9) of the double concave negative lens L22, and thereflected light rays are reflected again by the image plane I side lenssurface (a second-ghost-generating surface whose surface number is 8) ofthe negative meniscus lens L21 to reach the image plane I withgenerating ghost images. Incidentally, the first-ghost-generatingsurface 9 is a concave surface seen from the object side, and thesecond-ghost-generating surface 8 is a concave surface seen from theaperture stop S. With forming an antireflection coating corresponding toa broad wavelength range to such lens surfaces, it becomes possible toeffectively suppress ghost images and flare.

Example 5

FIG. 8 is a sectional view showing a lens configuration of a zoom lensaccording to Example 5 of the second embodiment of the presentapplication.

As shown in FIG. 8 , the zoom lens according to Example 5 of the secondembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, and a rear lens group G32having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved at first to the image side and then to the objectside, and the third lens group G3 is moved monotonously to the objectside with respect to the image plane I such that a distance between thefirst lens group G1 and the second lens group G2 increases, and adistance between the second lens group G2 and the third lens group G3decreases. Moreover, the front lens group G31, and the rear lens groupG32 are moved monotonously to the object side with respect to the imageplane I such that a distance between the front lens group G31 and therear lens group G32 decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side. The positivemeniscus lens L13 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by anegative meniscus lens L24 having a convex surface facing the image sidecemented with a positive meniscus lens L25 having a convex surfacefacing the image side. The negative meniscus lens L21 disposed to themost object side of the second lens group G2 is a compound typeaspherical lens whose object side lens surface is formed as anaspherical surface by applying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, a cemented lens constructed by a double convexpositive lens L33 cemented with a double concave negative lens L34, acemented lens constructed by a double concave negative lens L35 cementedwith a positive meniscus lens L36 having a convex surface facing theobject side, and a negative meniscus lens L37 having a concave surfacefacing the object side. The double concave negative lens L35 is a glassmold type aspherical lens whose object side lens surface is formed as anaspherical surface. The double convex positive lens L31 is the positivelens A′ satisfying conditional expressions (14) and (15).

The rear lens group G32 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L41, and acemented lens constructed by a double concave negative lens L42 cementedwith a double convex positive lens L43. The double convex positive lensL41 disposed to the most object side of the rear lens group G32 is aglass mold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L43 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 5of the second embodiment, an antireflection coating described later isapplied to the object side lens surface of the positive meniscus lensL13 in the first lens group G1 and the image side lens surface of thedouble convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to Example 5 ofthe second embodiment are listed in Table 5.

TABLE 5 (Specifications) zoom ratio = 15.696 W M T f= 18.53979 104.99746290.99204 FNO= 4.10702 5.39973 5.39939 ω= 38.99845 7.50128 2.73812 Y=14.20 14.20 14.20 TL= 160.00885 218.99165 237.79997 Bf= 39.1169389.39051 99.16649 (Lens Data) i r d nd νd OP ∞ ∞  1 123.95945 2.000001.850260 32.35  2 65.81889 9.30000 1.497820 82.52  3 −679.81898 0.10000 4 66.63494 6.20000 1.593190 67.87  5 419.93083  (d5)  6* 162.324160.15000 1.553890 38.09  7 146.07537 1.00000 1.834807 42.72  8 16.130356.55000  9 −35.27597 1.00000 1.882997 40.76 10 60.44503 0.10000 1137.37226 5.20000 1.846660 23.78 12 −32.72792 0.82143 13 −23.946281.00000 1.882997 40.76 14 −252.41497 2.00000 1.808090 22.79 15 −72.44788(d15) 16 ∞ 1.00000 Aperture stop S 17 36.72216 3.30000 1.593190 67.87 18−118.19629 0.10000 19 41.37679 3.15000 1.487490 70.41 20 −92.342920.10000 21 42.34033 3.80000 1.487490 70.41 22 −41.00357 1.00000 1.80518125.43 23 259.36092 3.81909 24* −63.64853 1.00000 1.806100 40.94 2522.00000 2.90000 1.805181 25.43 26 150.57815 4.20000 27 −45.824411.00000 1.882997 40.76 28 −215.98952 (d28) 29* 77.17936 3.15000 1.58913061.16 30 −37.11866 0.10000 31 −261.29488 1.00000 1.882997 40.76 3239.98076 4.40000 1.518229 58.93 33 −48.52092 (Bf) I ∞ (AsphericalSurface Data) Surface Number = 6 κ = −5.7774 A4 = 6.79980E−06 A6 =−2.52730E−08 A8 = 8.26150E−11 A10 = −1.02860E−13 Surface Number = 24 κ =2.8196 A4 = 4.59750E−06 A6 = 4.28350E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 29 κ = −6.5363 A4 = −1.95310E−05 A6 =1.79050E−08 A8 = −1.55070E−10 A10 = 4.13770E−13 (Variable Distances) W MT d5= 2.15153 45.02627 65.69297 d15= 40.45482 13.14016 2.00000 d28=8.84506 1.99420 1.50000 Bf= 39.11693 89.39051 99.16649 (Lens Group Data)Group ST Focal Length 1 1 103.25223 2 6 −15.13084 3 16 39.55369(W)35.07124(M) 34.78685(T) 31 16 44.76649 32 29 47.36030 (Values forConditional Expressions)  (2) f1/fw = 5.569  (3) f1/ft = 0.355  (4)Δ1/f1 = 0.753 (11) ndN = 1.850260 (L11) (12) νdN = 32.35 (L11) (14) ndA′= 1.593190 (L13) (14) ndA′ = 1.593190 (L31) (15) νdA′ = 67.87 (L13) (15)νdA′ = 67.87 (L31) (16) f3A′/f3 = 1.204 (L31)(W) (16) f3A′/f3 = 1.358(L31)(M) (16) f3A′/f3 = 1.369 (L31)(T) (17) f1A′/f1 = 1.285 (L13) (18)φ1A′/fw = 2.918 (φ1A′ = 54.10) (L13) (19) φ1A′/ft = 0.186 (φ1A′ =54.10)(L13) (20) νdB′ = 82.52 (L12) (21) f31A′/f31 = 1.064 (L31)

FIGS. 9A, 9B and 9C are graphs showing various aberrations of the zoomlens according to Example 5 of the second embodiment upon focusing on aninfinitely distant object, in which FIG. 9A is a wide-angle end state,FIG. 9B is an intermediate focal length state, and FIG. 9C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 5of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Example 6

FIG. 10 is a sectional view showing a lens configuration of a zoom lensaccording to Example 6 of the second embodiment of the presentapplication.

As shown in FIG. 10 , the zoom lens according to Example 6 of the secondembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side. The positivemeniscus lens L13 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side. The double convexpositive lens L31 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a compound type aspherical lens whose object side lenssurface is an aspherical surface formed by applying a resin layer.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L51, a doubleconvex positive lens L52, and a cemented lens constructed by a doubleconcave negative lens L53 cemented with a double convex positive lensL54. The double convex positive lens L51 disposed to the most objectside of the rear lens group G33 is a glass mold type aspherical lenswhose object side lens surface is an aspherical surface. Light rays comeout from the double convex positive lens L54 form an image on the imageplane I. In the zoom lens seen from another point of view according toExample 6 of the second embodiment, an antireflection coating describedlater is applied to the object side lens surface of the positivemeniscus lens L13 in the first lens group G1 and the object side lenssurface of the double concave negative lens L24 in the second lens groupG2.

Various values associated with the zoom lens according to Example 6 ofthe second embodiment are listed in Table 6.

TABLE 6 (Specifications) zoom ratio = 15.701 W M T f= 18.56060 104.65150291.42454 FNO= 3.57565 5.62482 5.81064 ω= 38.80191 7.44205 2.72113 Y=14.20 14.20 14.20 TL= 164.76435 225.28899 250.61470 Bf= 38.8470573.57929 86.64770 (Lens Data) i r d nd νd OP ∞ ∞  1 175.60560 2.200001.834000 37.16  2 67.43020 8.80000 1.497820 82.52  3 −587.78480 0.10000 4 72.27100 6.45000 1.593190 67.87  5 1826.13880  (d5)  6* 84.768700.10000 1.553890 38.09  7 73.93750 1.20000 1.834807 42.72  8 17.187306.95000  9 −36.98220 1.00000 1.816000 4 6.62 10 77.92630 0.15000 1136.63460 5.30000 1.784723 25.68 12 −36.63460 0.80000 13 −26.199101.00000 1.816000 46.62 14 63.73960 2.05000 1.808090 22.79 15 −643.27060(d15) 16 ∞ 1.00000 Aperture Stop S 17 65.83650 3.40000 1.593190 67.87 18−50.15460 0.10000 19 65.68170 2.45000 1.487490 70.41 20 −154.974300.10000 21 46.73330 4.20000 1.487490 70.41 22 −35.78330 1.00000 1.80809022.79 23 −191.93180 (d23) 24* −57.29660 0.20000 1.553890 38.09 25−59.72500 0.90000 1.696797 55.52 26 28.51000 2.15000 1.728250 28.46 2791.99760 4.14020 28 −32.89540 1.00000 1.729157 54.66 29 −144.33150 (d29)30* 6427.19190 4.65000 1.589130 61.18 31 −27.38180 0.10000 32 31.477605.85000 1.487490 70.41 33 −43.75390 1.45000 34 −113.58970 1.000001.882997 40.76 35 20.34810 5.30000 1.548141 45.79 36 −709.14530 (Bf) I ∞(Aspherical Surface Data) Surface Number = 6 κ = 1.0000 A4 = 2.88220E−06A6 = −2.29350E−11 A8 = −2.35280E−11 A10 = 9.21570E−14 Surface Number =24 κ = 1.0000 A4 = 4.32780E−06 A6 = 1.88460E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 30 κ = 1.0000 A4 = −1.36170E−05 A6 =−3.55860E−10 A8 = 1.83080E−11 A10 = −1.86790E−13 (Variable Distances) WM T d5= 2.15700 53.01000 76.25220 d15= 33.36360 11.30360 2.00000 d23=3.46820 9.64300 9.62460 d29= 11.83830 2.66290 1.00000 Bf= 38.8470573.57929 86.64770 (Lens Group Data) Group ST Focal Length 1 1 117.729372 6 −15.60945 3 16 40.44471(W) 33.95695(M) 32.70088(T) 31 16 27.35473 3224 −26.50041 33 30 35.20423 (Values for Conditional Expressions)  (2)f1/fw = 6.343  (3) f1/ft = 0.404  (4) Δ1/f1 = 0.729 (11) ndN = 1.834000(L11) (12) νdN = 37.16 (L11) (14) ndA′ = 1.593190 (L13) (14) ndA′ =1.593190 (L31) (15) νdA′ = 67.87 (L13) (15) νdA′ = 67.87 (L31) (16)f3A′/f3 = 1.200 (L31)(W) (16) f3A′/f3 = 1.429 (L31)(M) (16) f3A′/f3 =1.484 (L31)(T) (17) f1A′/f1 = 1.076 (L13) (18) φ1A′/fw = 2.909 (φ1A′ =54.00)(L13) (19) φ1A′/ft = 0.185 (φ1A′ = 54.00)(L13) (20) νdB′ = 82.52(L12) (21) f31A′/f31 = 1.774 (L31)

FIGS. 11A, 11B and 11C are graphs showing various aberrations of thezoom lens according to Example 6 of the second embodiment upon focusingon an infinitely distant object, in which FIG. 11A is a wide-angle endstate, FIG. 11B is an intermediate focal length state, and FIG. 11C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 6of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Example 7

FIG. 12 is a sectional view showing a lens configuration of a zoom lensaccording to Example 7 of the second embodiment of the presentapplication.

As shown in FIG. 12 , the zoom lens according to Example 7 of the secondembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side. The positivemeniscus lens L13 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side. The double convexpositive lens L31 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a compound type aspherical lens whose object side lenssurface is an aspherical surface by applying a resin layer.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 7of the second embodiment, an antireflection coating described later isapplied to the image side lens surface of the negative meniscus lens L21in the second lens group G2 and the object side lens surface of thedouble concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to Example 7 ofthe second embodiment are listed in Table 7.

TABLE 7 (Specifications) zoom ratio = 15.721 W M T f= 18.52363 104.52143291.21725 FNO= 3.60558 5.69344 5.89616 ω= 38.89095 7.41882 2.71146 Y=14.20 14.20 14.20 TL= 164.74420 225.48860 251.39424 Bf= 39.4425071.57530 83.10134 (Lens Data) i r d nd νd OP ∞ ∞  1 186.59960 2.200001.834000 37.17  2 69.08900 8.80000 1.497820 82.56  3 −494.44545 0.10000 4 73.40222 6.45000 1.593190 67.87  5 2016.71160  (d5)  6* 84.850000.10000 1.553890 38.09  7 74.02192 1.20000 1.834810 42.72  8 17.097476.95000  9 −37.97970 1.00000 1.816000 46.63 10 77.67127 0.15000 1136.26557 5.30000 1.784720 25.68 12 −36.26557 0.80000 13 −25.696421.00000 1.816000 46.63 14 66.08300 2.05000 1.808090 22.79 15 −666.70366(d15) 16 ∞ 1.00000 Aperture Stop S 17 68.30727 3.40000 1.593190 67.87 18−47.99596 0.10000 19 68.52367 2.45000 1.487490 70.45 20 −136.983920.10000 21 46.52671 4.20000 1.487490 70.45 22 −36.16400 1.00000 1.80809022.79 23 −202.95328 (d23) 24* −55.09840 0.20000 1.553890 38.09 25−57.24715 0.90000 1.696800 55.52 26 28.15100 2.15000 1.728250 28.46 2787.70856 4.35000 28 −26.69877 1.00000 1.729160 54.66 29 −76.47707 (d29)30* −333.89500 4.65000 1.589130 61.18 31 −24.64395 0.10000 32 31.196255.85000 1.487490 70.45 33 −43.38887 1.45000 34 −109.71645 1.000001.883000 40.77 35 20.29920 5.30000 1.548140 45.79 36 −808.81321 (Bf) I ∞(Aspherical Surface Data) Surface Number = 6 κ = 1.0000 A4 = 3.13350E−06A6 = 4.73080E−10 A8 = −3.40500E−11 A10 = 1.16620E−13 Surface Number = 24κ = 1.0000 A4 = 5.24030E−06 A6 = −2.00730E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 30 κ = 1.0000 A4 = −1.54020E−05 A6 =1.69500E−09 A8 = 1.34490E−11 A10 = −2.07220E−13 (Variable Distances) W MT d5= 2.15700 53.25650 76.94960 d15= 33.80140 11.31350 2.00000 d23=3.45650 11.60170 13.04330 d29= 10.58680 2.44160 1.00000 Bf= 39.4425071.57530 83.10134 (Lens Group Data) Group ST Focal Length 1 1 118.969102 6 −15.62542 3 16 40.08868(W) 33.90635(M) 32.38356(T) 31 16 27.17463 3224 −25.41506 33 30 34.39022 (Values for Conditional Expressions)  (2)f1/fw = 6.423  (3) f1/ft = 0.409  (4) Δ1/f1 = 0.728 (11) ndN = 1.834000(L11) (12) νdN = 37.17 (L11) (14) ndA′ = 1.593190 (L13) (14) ndA′ =1.593190 (L31) (15) νdA′ = 67.87 (L13) (15) νdA′ = 67.87 (L31) (16)f3A′/f3 = 1.198 (L31)(W) (16) f3A′/f3 = 1.417 (L31)(M) (16) f3A′/f3 =l.484 (L31)(T) (17) f1A′/f1 = 1.078 (L13) (18) φ1A′/fw = 2.915 (φ1A′ =54.00)(L13) (19) φ1A′/ft = 0.185 (φ1A′ = 54.00)(L13) (20) νdB′ = 82.52(L12) (21) f31A′/f31 = 1.768 (L31)

FIGS. 13A, 13B and 13C are graphs showing various aberrations of thezoom lens according to Example 7 of the second embodiment upon focusingon an infinitely distant object, in which FIG. 13A is a wide-angle endstate, FIG. 13B is an intermediate focal length state, and FIG. 13C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 7of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Example 8

FIG. 6 is a sectional view showing a lens configuration of a zoom lensaccording to Example 8 of the second embodiment of the presentapplication.

As shown in FIG. 6 , the zoom lens according to Example 8 of the secondembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a double convexpositive lens L13.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side. The double convexpositive lens L31 is the positive lens A′ satisfying conditionalexpressions (14) and (15).

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a glass mold type aspherical lens whose object side lenssurface is an aspherical surface.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 8of the second embodiment, an antireflection coating described later isapplied to the image side lens surface of the double convex positivelens L12 in the first lens group G1 and the object side lens surface ofthe double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to Example 8 ofthe second embodiment are listed in Table 8.

TABLE 8 (Specifications) zoom ratio = 15.714 W M T f= 18.55566 103.95947291.57591 FNO= 3.63338 5.62730 5.88308 ω= 38.94112 7.46798 2.71133 Y=14.20 14.20 14.20 TL= 163.38092 225.17861 252.25324 Bf= 39.1716270.49651 82.47674 (Lens Data) i r d nd νd OP ∞ ∞  1 193.38060 2.000001.883000 40.77  2 66.83560 9.23080 1.437000 95.00  3 −341.14920 0.10000 4 68.78950 6.98760 1.603000 65.47  5 −2649.89320  (d5)  6* 84.768700.15000 1.553890 38.09  7 73.93750 1.20000 1.834810 42.72  8 16.948206.42970  9 −53.17850 1.00000 1.816000 46.63 10 46.70940 0.15000 1130.63920 5.37880 1.761820 26.56 12 −48.96880 1.39690 13 −24.422501.00000 1.816000 46.63 14 69.10450 2.52380 1.808090 22.79 15 −121.94360(d15) 16 ∞ 1.00000 Aperture Stop S 17 66.08180 3.43590 1.592820 68.69 18−50.37120 0.10000 19 59.42650 2.78060 1.487490 70.45 20 −108.478700.10000 21 49.67940 4.11660 1.487490 70.45 22 −33.83640 1.00000 1.80809022.79 23 −167.67900 (d23) 24* −64.89240 1.00000 1.693500 53.22 2527.12400 2.14440 1.761820 26.56 26 65.84410 4.73170 27 −25.14850 1.000001.729160 54.66 28 −73.72860 (d28) 29* −448.31420 3.90050 1.589130 61.1830 −23.64180 0.10000 31 37.43750 4.98090 1.487490 70.45 32 −44.964101.73250 33 −102.62990 1.00000 1.883000 40.77 34 23.17730 4.511701.548140 45.79 35 −619.02620 (Bf) I ∞ (Aspherical Surface Data) SurfaceNumber = 6 κ = 1.0000 A4 = 4.16398E−06 A6 = −7.55222E−09 A8 =−2.91689E−12 A10 = 5.62106E−14 Surface Number = 24 κ = 1.0000 A4 =3.83569E−06 A6 = −1.03578E−09 A8 = 0.00000E+00 A10 = 0.00000E+00 SurfaceNumber = 29 κ = 1.0000 A4 = −1.60868E−05 A6 = 8.16360E−09 A8 =−3.55020E−11 A10 = 7.60058E−14 (Variable Distances) W M T d5= 2.1270055.32280 79.77200 d15= 34.07780 11.35470 2.00000 d23= 3.36200 10.6767011.82210 d2= 9.46010 2.14550 1.00000 Bf= 39.17162 70.49651 82.47674(Lens Group Data) Group ST Focal Length 1 1 120.77885 2 6 −15.59572 3 1639.12629(W) 32.72813(M) 31.47773(T) 31 16 26.38558 32 24 −24.49396 33 2934.76717 (Values for Conditional Expressions)  (2) f1/fw = 6.509  (3)f1/ft = 0.414  (4) Δ1/f1 = 0.736 (11) ndN = 1.883000 (L11) (12) νdN =40.77 (L11) (14) ndA′ = 1.592820 (L31) (15) νdA′ = 68.69 (L31) (16)f3A′/f3 = 1.246 (L31)(W) (16) f3A′/f3 = 1.490 (L31)(M) (16) f3A′/f3 =1.549 (L31)(T) (20) νdB′ = 95.00 (L12) (21) f31A′/f31 = 1.848 (L31)

FIGS. 7A, 7B and 7C are graphs showing various aberrations of the zoomlens according to Example 8 of the second embodiment upon focusing on aninfinitely distant object, in which FIG. 7A is a wide-angle end state,FIG. 7B is an intermediate focal length state, and FIG. 7C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 8of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

Then, an outline of a method for manufacturing a zoom lens according tothe second embodiment is explained.

FIG. 25 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the second embodiment.

The method for manufacturing a zoom lens according to the secondembodiment is a method for manufacturing a zoom lens including, in orderfrom an object side along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, and a third lens group G3 having positive refractivepower, and being constructed such that at least one optical surface inthe first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process, the method including stepsS21 through S23 shown in FIG. 25 .

Step S21: disposing the first lens group G1, the second lens group G2and the third lens group G3 movably such that upon zooming from awide-angle end state to a telephoto end state, a distance between thefirst lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases.

Step S22: disposing a positive lens A′ satisfying the followingconditional expressions (14) and (15):1.540<ndA′  (14)66.5<νdA′  (15)where ndA′ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of the positive lens A′, and νdA′ denotes an Abbe numberat d-line (wavelength λ=587.6 nm) of a material of the positive lens A′.

Step S23: disposing each lens with satisfying the following conditionalexpression (2):3.90<f1/fw<11.00  (2)where fw denotes a focal length of the zoom lens in the wide-angle endstate, and f1 denotes a focal length of the first lens group.

With this method for manufacturing a zoom lens according to the secondembodiment, it becomes possible to manufacture a zoom lens havingexcellent optical performance with suppressing variations in aberrationsand ghost images and flare.

Third Embodiment

A zoom lens according to a third embodiment of the present applicationis explained below.

A zoom lens according to the third embodiment of the present applicationincludes, in order from an object side along an optical axis, a firstlens group having positive refractive power, a second lens group havingnegative refractive power, and a third lens group having positiverefractive power. Upon zooming from a wide-angle end state to atelephoto end state, a distance between the first lens group and thesecond lens group increases, and a distance between the second lensgroup and the third lens group decreases. With this configuration, itbecomes possible to realize a zoom lens, and, at the same time, suppressvariation in distortion generated upon zooming.

In a zoom lens according to the third embodiment, the first lens groupincludes a plurality of positive lenses that satisfy the followingconditional expressions (22) and (23), and satisfies the followingconditional expression (3):66.5<νdA″ when 1.540≤ndA″75.0<νdA″ when ndA″≤1.540  (22)4.75<f1/fw<11.0  (23)0.28<f1/ft<0.52  (3)where ndA″ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of each of a plurality of positive lenses in the firstlens group, νdA″ denotes an Abbe number at d-line (wavelength λ=587.6nm) of a material of each of a plurality of positive lenses in the firstlens group, fw denotes a focal length of the zoom lens in the wide-angleend state, ft denotes a focal length of the zoom lens in the telephotoend state, and f1 denotes a focal length of the first lens group.

Conditional expression (22) defines an optimum Abbe number of thematerial of each of the plurality of positive lenses in the first lensgroup, and is for realizing high optical performance with suppressingvariations in longitudinal chromatic aberration and lateral chromaticaberration generated upon zooming from the wide-angle end state to thetelephoto end state.

When the value νdA″ is equal to or falls below the lower limit ofconditional expression (22), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

In order to secure the effect of the third embodiment, it is preferableto set the lower limit of conditional expression (22) to 67.5 when 1.540ndA″. In order to secure the effect of the third embodiment, it ispreferable to set the lower limit of conditional expression (22) to 80.5when ndA″<1.540.

Conditional expression (23) defines an optimum range of the focal lengthof the first lens group, and is for realizing high optical performancewith suppressing variations in chromatic aberration and off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state.

When the ratio f1/fw is equal to or falls below the lower limit ofconditional expression (23), refractive power of the first lens groupbecomes strong, so that it becomes difficult to suppress variation inlateral chromatic aberration and off-axis aberrations, in particular,astigmatism. As a result, high optical performance cannot be realized.

On the other hand, when the ratio f1/fw is equal to or exceeds the upperlimit of conditional expression (23), refractive power of the first lensgroup becomes weak, so that in order to obtain a given zoom ratio, amoving amount of the first lens group with respect to the image planehas to be large. Accordingly, variation in the height from the opticalaxis of the off-axis ray becomes large. As a result, variations inlateral chromatic aberration and off-axis aberrations, in particular,astigmatism cannot be suppressed, so that high optical performancecannot be realized.

In order to secure the effect of the third embodiment, it is preferableto set the lower limit of conditional expression (23) to 5.10.

In order to secure the effect of the third embodiment, it is preferableto set the upper limit of conditional expression (23) to 8.80. In orderto further secure the effect of the third embodiment, it is mostpreferable to set the upper limit of conditional expression (23) to7.60.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (3)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens according to the third embodiment, the followingconditional expression (4) is preferably satisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state, and is for realizinghigh optical performance with suppressing variations in chromaticaberration and off-axis aberrations generated upon zooming. However,conditional expression (4) has already been explained above, so thatduplicated explanations are omitted.

In a zoom lens according to the third embodiment, the followingconditional expression (24) is preferably satisfied:0.65<f1A″/f1<1.75  (24)where f1A″ denotes a focal length of each of the plurality of positivelenses in the first lens group.

Conditional expression (24) defines optimum focal length of each of theplurality of positive lenses in the first lens group, and is forrealizing high optical performance with suppressing variations inchromatic aberration and off-axis aberrations generated upon zooming.

When the ratio f1A″/f1 is equal to or falls below the lower limit ofconditional expression (24), refractive power of each of the pluralityof positive lens becomes strong, so that upon zooming from thewide-angle end state to the telephoto end state, variation in refractivepower in accordance with variation in the height from the optical axisof the off-axis ray passing through the first lens group becomes large.As a result, it becomes difficult to suppress variations in lateralchromatic aberration and off-axis aberrations, in particular,astigmatism, so that high optical performance cannot be realized.

On the other hand, when the ratio f1A″/f1 is equal to or exceeds theupper limit of conditional expression (24), refractive power of each ofthe plurality of positive lens becomes weak, so that it becomesdifficult to suppress variations in chromatic aberration and off-axisaberrations, in particular, astigmatism. Accordingly, high opticalperformance cannot be realized.

In order to secure the effect of the third embodiment, it is preferableto set the lower limit of conditional expression (24) to 0.80.

In order to secure the effect of the third embodiment, it is preferableto set the upper limit of conditional expression (24) to 1.35.

In a zoom lens according to the third embodiment, the followingconditional expression (25) is preferably satisfied:1.75<φ1A″/fw<4.50  (25)where φ1A″ denotes an effective diameter of each of the plurality ofpositive lenses in the first lens group.

Conditional expression (25) defines an optimum effective diameter ofeach of the plurality of positive lenses in the first lens group, and isfor realizing high optical performance with suppressing variations inchromatic aberration and off-axis aberrations generated upon zooming.

When the ratio φ1A″/fw is equal to or falls below the lower limit ofconditional expression (25), upon zooming from the wide-angle end stateto the telephoto end state, variation in the height from the opticalaxis of the off-axis ray passing through the plurality of positivelenses in the first lens group becomes small, so that it becomesdifficult to suppress variations in off-axis aberrations, in particular,astigmatism. Accordingly, high optical performance cannot be realized.

On the other hand, when the ratio φ1A″/fw is equal to or exceeds theupper limit of conditional expression (25), upon zooming from thewide-angle end state to the telephoto end state, variation in the heightfrom the optical axis of the off-axis ray passing through the pluralityof positive lenses in the first lens group becomes large, so that itbecomes difficult to suppress variations in lateral chromatic aberrationand off-axis aberrations, in particular, astigmatism. Accordingly, highoptical performance cannot be realized.

In order to secure the effect of the third embodiment, it is preferableto set the lower limit of conditional expression (25) to 2.45.

In order to secure the effect of the third embodiment, it is preferableto set the upper limit of conditional expression (25) to 3.80.

In a zoom lens according to the third embodiment, the number of theplurality of positive lenses in the first lens group is preferably two.

With this configuration, it becomes possible to suppress the thicknessof the first lens group, so that it becomes possible to suppressvariation in the height from the optical axis of the off-axis raypassing through the most object side surface of the first lens group. Asa result, it becomes possible to suppress variations in off-axisaberrations, in particular, astigmatism, so that high opticalperformance can be realized.

In a zoom lens according to the third embodiment, the first lens grouppreferably include a negative lens that satisfies the followingconditional expressions (11) and (12):1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (11) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (12)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens according to the third embodiment, the number of thenegative lens in the first lens group is preferably one.

With this configuration, it becomes possible to suppress the thicknessof the first lens group, so that upon zooming from the wide-angle endstate to the telephoto end state, variation in the height from theoptical axis of the off-axis ray passing through the most object sidesurface of the first lens group can be suppressed. Variations inoff-axis aberrations, in particular, astigmatism can be suppressed, sothat high optical performance can be realized.

In a zoom lens according to the third embodiment, the third lens grouppreferably satisfies the following conditional expression (26):65.5<νd3  (26)where νd3 denotes an Abbe number at d-line (wavelength λ=587.6 nm) ofthe material of the positive lens in the third lens group.

Conditional expression (26) defines an optimum Abbe number of thematerial of the positive lens in the third lens group, and for realizinghigh optical performance with suppressing variation in chromaticaberration generated upon zooming from the wide-angle end state to thetelephoto end state.

When the value νd3 is equal to or falls below the lower limit ofconditional expression (26), it becomes difficult to suppress variationsin longitudinal chromatic aberration and lateral chromatic aberration.The material becomes a one having small anomalous dispersion, so thatvariation in secondary order of chromatic aberration becomes difficultto be suppressed. In addition, longitudinal chromatic aberration andlateral chromatic aberration in visible light range become large in thetelephoto end state, so that high optical performance cannot beobtained.

In a zoom lens according to the third embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power and a rear lens group havingpositive refractive power, and a distance between the front lens groupand the rear lens group decreases upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens according to the third embodiment, it is preferable thatthe third lens group includes, in order from the object side, a frontlens group having positive refractive power, a middle lens group havingnegative refractive power, and a rear lens group having positiverefractive power, and a distance between the front lens group and themiddle lens group varies, and a distance between the middle lens groupand the rear lens group varies upon zooming from the wide-angle endstate to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens according to the third embodiment, it is preferable thata distance between the front lens group and the middle lens groupincreases, and a distance between the middle lens group and the rearlens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

Then, a zoom lens seen from another point of view according to the thirdembodiment of the present application is explained below.

A zoom lens seen from another point of view according to the thirdembodiment of the present application includes, in order from an objectside along an optical axis, a first lens group having positiverefractive power, a second lens group having negative refractive power,and a third lens group having positive refractive power. Upon zoomingfrom a wide-angle end state to a telephoto end state, a distance betweenthe first lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases. Withthis configuration, it becomes possible to realize a zoom lens, and, atthe same time, suppress variation in distortion generated upon zooming.

In a zoom lens seen from another point of view according to the thirdembodiment, the first lens group includes a plurality of positive lensesthat satisfy the following conditional expressions (22) and (23), andsatisfies the following conditional expression (3):66.5<νdA″ when 1.540≤ndA″75.0<νdA″ when ndA″≤1.540  (22)4.75<f1/fw<11.0  (23)0.28<f1/ft<0.52  (3)where ndA″ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of each of a plurality of positive lenses in the firstlens group, νdA″ denotes an Abbe number at d-line (wavelength λ=587.6nm) of a material of each of a plurality of positive lenses in the firstlens group, fw denotes a focal length of the zoom lens in the wide-angleend state, ft denotes a focal length of the zoom lens in the telephotoend state, and f1 denotes a focal length of the first lens group.

Conditional expression (22) defines an optimum Abbe number of thematerial of each of the plurality of positive lenses in the first lensgroup, and is for realizing high optical performance with suppressingvariations in longitudinal chromatic aberration and lateral chromaticaberration generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (22) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (23) defines an optimum range of the focal lengthof the first lens group, and is for realizing high optical performancewith suppressing variations in chromatic aberration and off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (23) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (3) defines an appropriate range of an optimumfocal length of the first lens group, and is for realizing high opticalperformance with suppressing variations in chromatic aberration andoff-axis aberrations generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (3)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the thirdembodiment of the present application, at least one optical surfaceamong the first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process. With this configuration, azoom lens seen from another point of view according to the thirdembodiment of the present application makes it possible to suppressghost images and flare generated by the light rays from the objectreflected from the optical surfaces, thereby realizing excellent opticalperformance.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the antireflectioncoating is a multilayer film, and the layer formed by the wet process ispreferably the outermost layer among the layers composing the multilayerfilm. With this configuration, since difference in refractive index withrespect to the air can be small, reflection of light can be small, sothat ghost images and flare can further be suppressed.

In a zoom lens seen from another point of view according to the thirdembodiment of the present application, when a refractive index at d-lineof the layer formed by the wet process is denoted by nd, the refractiveindex nd is preferably 1.30 or less. With this configuration, sincedifference in refractive index with respect to the air can be small,reflection of light can be small, so that ghost images and flare canfurther be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an aperture stop. Since reflection light rays areliable to be generated on a concave surface seen from the aperture stopamong optical surfaces in the first lens group and the second lensgroup, with applying the antireflection coating on such an opticalsurface, ghost images and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the thirdembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is animage side lens surface. Since the image side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

In a zoom lens seen from another point of view according to the thirdembodiment, it is desirable that, the concave surface on which theantireflection coating is applied as seen from the aperture stop is anobject side lens surface. Since the object side concave surface as seenfrom the aperture stop among optical surfaces in the first lens groupand the second lens group tends to generate reflection light, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the optical surface onwhich the antireflection coating is formed is preferably a concavesurface seen from an object side. Since reflection light rays are liableto be generated on a concave surface seen from the object among opticalsurfaces in the first lens group and the second lens group, withapplying the antireflection coating on such an optical surface, ghostimages and flare can effectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side secondlens from the most object side lens in the first lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side second lens from the most object side lens inthe first lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidesecond lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side second lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an image side lens surface of the image side thirdlens from the most object side lens in the second lens group. Sincereflection light rays are liable to be generated on the image side lenssurface of the image side third lens from the most object side lens inthe second lens group, with applying the antireflection coating on suchan optical surface, ghost images and flare can effectively besuppressed.

Moreover, in a zoom lens seen from another point of view according tothe third embodiment of the present application, the concave opticalsurface seen from the object on which the antireflection coating isformed is preferably an object side lens surface of the image sidefourth lens from the most object side lens in the second lens group.Since reflection light rays are liable to be generated on the objectside lens surface of the image side fourth lens from the most objectside lens in the second lens group, with applying the antireflectioncoating on such an optical surface, ghost images and flare caneffectively be suppressed.

In a zoom lens seen from another point of view according to the thirdembodiment, the antireflection coating may also be formed by a dryprocess etc without being limited to the wet process. On this occasion,it is preferable that the antireflection coating contains at least onelayer of which the refractive index is equal to 1.30 or less. Thus, thesame effects as in the case of using the wet process can be obtained byforming the antireflection coating based on the dry process etc. Notethat at this time the layer of which the refractive index is equal to1.30 or less is preferably the layer of the outermost surface of thelayers composing the multi layer film.

In a zoom lens seen from another point of view according to the thirdembodiment, the following conditional expression (4) is preferablysatisfied:0.25<Δ1/f1<1.10  (4)where Δ1 denotes a moving amount of the first lens group with respect tothe image plane upon zooming from the wide-angle end state to thetelephoto end state.

Conditional expression (4) defines an optimum moving amount of the firstlens group with respect to the image plane upon zooming from thewide-angle end state to the telephoto end state. However, conditionalexpression (4) has already been explained above, so that duplicatedexplanations are omitted.

In a zoom lens seen from another point of view according to the thirdembodiment, the following conditional expression (24) is preferablysatisfied:0.65<f1A″/f1<1.75  (24)where f1A″ denotes a focal length of each of the plurality of positivelenses in the first lens group.

Conditional expression (24) defines optimum focal length of each of theplurality of positive lenses in the first lens group, and is forrealizing high optical performance with suppressing variations inchromatic aberration and off-axis aberrations generated upon zooming.However, conditional expression (24) has already been explained above,so that duplicated explanations are omitted.

In a zoom lens seen from another point of view according to the thirdembodiment, the following conditional expression (25) is preferablysatisfied:1.75<φ1A″/fw<4.50  (25)where φ1A″ denotes an effective diameter of each of the plurality ofpositive lenses in the first lens group.

Conditional expression (25) defines an optimum effective diameter ofeach of the plurality of positive lenses in the first lens group, and isfor realizing high optical performance with suppressing variations inchromatic aberration and off-axis aberrations generated upon zooming.However, conditional expression (25) has already been explained above,so that duplicated explanations are omitted.

In a zoom lens seen from another point of view according to the thirdembodiment, the number of the plurality of positive lenses in the firstlens group is preferably two.

With this configuration, it becomes possible to suppress the thicknessof the first lens group, so that it becomes possible to suppressvariation in the height from the optical axis of the off-axis raypassing through the most object side surface of the first lens group. Asa result, it becomes possible to suppress variations in off-axisaberrations, in particular, astigmatism, so that high opticalperformance can be realized.

In a zoom lens seen from another point of view according to the thirdembodiment, the first lens group preferably include a negative lens thatsatisfies the following conditional expressions (11) and (12):1.750<ndN  (11)28.0<νdN<50.0  (12)where ndN denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of a negative lens in the first lens group, and νdNdenotes an Abbe number at d-line (wavelength λ=587.6 nm) of the materialof the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of the refractiveindex in the negative lens in the first lens group, and is for realizinghigh optical performance with suppressing variations in off-axisaberrations generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (11) has alreadybeen explained above, so that duplicated explanations are omitted.

Conditional expression (12) defines an optimum Abbe number of thematerial of the negative lens in the first lens group, and is forrealizing high optical performance with suppressing variation inchromatic aberration generated upon zooming from the wide-angle endstate to the telephoto end state. However, conditional expression (12)has already been explained above, so that duplicated explanations areomitted.

In a zoom lens seen from another point of view according to the thirdembodiment, the number of the negative lens in the first lens group ispreferably one.

With this configuration, it becomes possible to suppress the thicknessof the first lens group, so that upon zooming from a wide-angle endstate to a telephoto end state it becomes possible to suppress variationin the height from the optical axis of the off-axis ray passing throughthe most object side surface of the first lens group. As a result, itbecomes possible to suppress variations in off-axis aberrations, inparticular, astigmatism, so that high optical performance can berealized.

In a zoom lens seen from another point of view according to the thirdembodiment, the third lens group preferably satisfies the followingconditional expression (26):65.5<νd3  (26)where νd3 denotes an Abbe number at d-line (wavelength λ=587.6 nm) ofthe material of the positive lens in the third lens group.

Conditional expression (26) defines an optimum Abbe number of thematerial of the positive lens in the third lens group, and for realizinghigh optical performance with suppressing variation in chromaticaberration generated upon zooming from the wide-angle end state to thetelephoto end state. However, conditional expression (26) has alreadybeen explained above, so that duplicated explanations are omitted.

In a zoom lens seen from another point of view according to the thirdembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power and a rear lens group having positive refractive power,and a distance between the front lens group and the rear lens groupdecreases upon zooming from the wide-angle end state to the telephotoend state.

With this configuration, zooming efficiency of the third lens group canbe enhanced better than a configuration that the third lens group ismoved in a body upon zooming. Moreover, high optical performance can berealized with suppressing variations in spherical aberration, coma andastigmatism.

In a zoom lens seen from another point of view according to the thirdembodiment, it is preferable that the third lens group includes, inorder from the object side, a front lens group having positiverefractive power, a middle lens group having negative refractive power,and a rear lens group having positive refractive power, and a distancebetween the front lens group and the middle lens group varies, and adistance between the middle lens group and the rear lens group variesupon zooming from the wide-angle end state to the telephoto end state.

With this configuration, variations in aberrations generated in thethird lens group can be suppressed better than a configuration that thethird lens group is moved in a body upon zooming, so that high opticalperformance can be realized with suppressing in particular sphericalaberration, coma and astigmatism.

In a zoom lens seen from another point of view according to the thirdembodiment, it is preferable that upon zooming from a wide-angle endstate to a telephoto end state a distance between the front lens groupand the middle lens group increases, and a distance between the middlelens group and the rear lens group decreases.

With this configuration, zooming efficiency of the third lens group canbe enhanced, so that high optical performance can be realized withsuppressing variations in spherical aberration, coma and astigmatism.

Then, a zoom lens according to each Example of the third embodiment isexplained below with reference to accompanying drawings. Incidentally,detailed explanation of an antireflection coating will be explainedseparately after Example 12 of the third embodiment.

Example 9

FIG. 12 is a sectional view showing a lens configuration of a zoom lensaccording to Example 9 of the third embodiment of the presentapplication.

As shown in FIG. 12 , the zoom lens according to Example 9 of the thirdembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side.

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a compound type aspherical lens whose object side lenssurface is an aspherical surface by applying a resin layer.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a positive meniscus lens L51 having a concavesurface facing the object side, a double convex positive lens L52, and acemented lens constructed by a double concave negative lens L53 cementedwith a double convex positive lens L54. The positive meniscus lens L51disposed to the most object side of the rear lens group G33 is a glassmold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 9of the third embodiment, an antireflection coating described later isapplied to the image side lens surface of the negative meniscus lens L21in the second lens group G2 and the object side lens surface of thedouble concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to Example 9 ofthe third embodiment are listed in Table 9.

TABLE 9 (Specifications) zoom ratio = 15.721 W M T f = 18.52363104.52143 291.21725 FNO = 3.60558 5.69344 5.89616 ω = 38.89095 7.418822.71146 Y = 14.20 14.20 14.20 TL = 164.74420 225.48860 251.39424 Bf =39.44250 71.57530 83.10134 (Lens Data) i r d nd νd OP ∞ ∞  1 186.599602.20000 1.834000 37.17  2 69.08900 8.80000 1.497820 82.56  3 −494.445450.10000  4 73.40222 6.45000 1.593190 67.87  5 2016.71160  (d5)  6*84.85000 0.10000 1.553890 38.09  7 74.02192 1.20000 1.834810 42.72  817.09747 6.95000  9 −37.97970 1.00000 1.816000 46.63 10 77.67127 0.1500011 36.26557 5.30000 1.784720 25.68 12 −36.26557 0.80000 13 −25.696421.00000 1.816000 46.63 14 66.08300 2.05000 1.808090 22.79 15 −666.70366(d15) 16 ∞ 1.00000 Aperture Stop S 17 68.30727 3.40000 1.593190 67.87 18−47.99596 0.10000 19 68.52367 2.45000 1.487490 70.45 20 −136.983920.10000 21 46.52671 4.20000 1.487490 70.45 22 −36.16400 1.00000 1.80809022.79 23 −202.95328 (d23) 24* −55.09840 0.20000 1.553890 38.09 25−57.24715 0.90000 1.696800 55.52 26 28.15100 2.15000 1.728250 28.46 2787.70856 4.35000 28 −26.69877 1.00000 1.729160 54.66 29 −76.47707 (d29)30* −333.89500 4.65000 1.589130 61.18 31 −24.64395 0.10000 32 31.196255.85000 1.487490 70.45 33 −43.38887 1.45000 34 −109.71645 1.000001.883000 40.77 35 20.29920 5.30000 1.548140 45.79 36 −808.81321 (Bf) I ∞(Aspherical Surface Data) Surface Number = 6 κ = 1.0000 A4 = 3.13350E−06A6 = 4.73080E−10 A8 = −3.40500E−11 A10 = 1.16620E−13 Surface Number = 24κ = 1.0000 A4 = 5.24030E−06 A6 = −2.00730E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 30 κ = 1.0000 A4 = −1.54020E−05 A6 =1.69500E−09 A8 = 1.34490E−11 A10 = −2.07220E−13 (Variable Distances) W MT d5 = 2.15700 53.25650 76.94960 d15 = 33.80140 11.31350 2.00000 d23 =3.45650 11.60170 13.04330 d29 = 10.58680 2.44160 1.00000 Bf = 39.4425071.57530 83.10134 (Lens Group Data) Group ST Focal Length 1 1 118.969102 6 −15.62542 3 16 40.08868(W) 33.90635(M) 32.38356(T) 31 16 27.17463 3224 −25.41506 33 30 34.39022 (Values for Conditional Expressions)  (3)f1/ft = 0.409  (4) Δ1/f1 = 0.728 (11) ndN = 1.834000 (L11) (12) νdN =37.17 (L11) (22) ndA″ = 1.497820 (L12) νdA″ = 82.56 (L12) (22) ndA″ =1.593190 (L13) νdA″ = 67.87 (L13) (23) f1/fw = 6.423 (24) f1A″/f1 =1.029 (L12) (24) f1A″/f1 = 1.078 (L13) (25) φ1A″/fw = 3.100 (φ1A″ =57.42)(L12) (25) φ1A″/fw = 2.915 (φ1A″ = 54.00)(L13) (26) νd3 = 67.87(L31)

FIGS. 13A, 13B and 13C are graphs showing various aberrations of thezoom lens according to Example 9 of the third embodiment upon focusingon an infinitely distant object, in which FIG. 13A is a wide-angle endstate, FIG. 13B is an intermediate focal length state, and FIG. 13C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example 9of the second embodiment shows superb optical performance as a result ofgood corrections to various aberrations.

FIG. 14 is a sectional view showing the lens configuration of the lenssystem seen from another point of view according to Example 9 of thethird embodiment and is an explanatory view, in which light raysreflected from a first-ghost-generating surface are reflected by asecond-ghost-generating surface.

As shown in FIG. 14 , when light rays BM from an object are incident onthe zoom lens, the rays are reflected by the object side lens surface (afirst-ghost-generating surface whose surface number is 9) of the doubleconcave negative lens L22, and the reflected light rays are reflectedagain by the image plane I side lens surface (a second-ghost-generatingsurface whose surface number is 8) of the negative meniscus lens L21 toreach the image plane I with generating ghost images. Incidentally, thefirst-ghost-generating surface 9 is a concave surface seen from theobject side, and the second-ghost-generating surface 8 is a concavesurface seen from the aperture stop S. With forming an antireflectioncoating corresponding to a broad wavelength range to such lens surfaces,it becomes possible to effectively suppress ghost images and flare.

Example 10

FIG. 8 is a sectional view showing a lens configuration of a zoom lensaccording to Example 10 of the third embodiment of the presentapplication.

As shown in FIG. 8 , the zoom lens according to Example 10 of the thirdembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, and a rear lens group G32having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved at first to the image side and then to the objectside, and the third lens group G3 is moved monotonously to the objectside with respect to the image plane I such that a distance between thefirst lens group G1 and the second lens group G2 increases, and adistance between the second lens group G2 and the third lens group G3decreases. Moreover, the front lens group G31, and the rear lens groupG32 are moved monotonously to the object side with respect to the imageplane I such that a distance between the front lens group G31 and therear lens group G32 decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by anegative meniscus lens L24 having a convex surface facing the image sidecemented with a positive meniscus lens L25 having a convex surfacefacing the image side. The negative meniscus lens L21 disposed to themost object side of the second lens group G2 is a compound typeaspherical lens whose object side lens surface is formed as anaspherical surface by applying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, a cemented lens constructed by a double convexpositive lens L33 cemented with a double concave negative lens L34, acemented lens constructed by a double concave negative lens L35 cementedwith a positive meniscus lens L36 having a convex surface facing theobject side, and a negative meniscus lens L37 having a concave surfacefacing the object side. The double concave negative lens L35 is a glassmold type aspherical lens whose object side lens surface is formed as anaspherical surface.

The rear lens group G32 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L41, and acemented lens constructed by a double concave negative lens L42 cementedwith a double convex positive lens L43. The double convex positive lensL41 disposed to the most object side of the rear lens group G32 is aglass mold type aspherical lens whose object side lens surface is anaspherical surface. Light rays come out from the double convex positivelens L43 form an image on the image plane I.

In the zoom lens seen from another point of view according to Example 10of the third embodiment, an antireflection coating described later isapplied to the object side lens surface of the positive meniscus lensL13 in the first lens group G1 and the image side lens surface of thedouble convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to Example 10 ofthe third embodiment are listed in Table 10.

TABLE 10 (Specifications) zoom ratio = 15.696 W M T f = 18.53979104.99746 290.99204 FNO = 4.10702 5.39973 5.39939 ω = 38.99845 7.501282.73812 Y = 14.20 14.20 14.20 TL = 160.00885 218.99165 237.79997 Bf =39.11693 89.39051 99.16649 (Lens Data) i r d nd νd OP ∞ ∞  1 123.959452.00000 1.850260 32.35  2 65.81889 9.30000 1.497820 82.52  3 −679.818980.10000  4 66.63494 6.20000 1.593190 67.87  5 419.93083  (d5)  6*162.32416 0.15000 1.553890 38.09  7 146.07537 1.00000 1.834807 42.72  816.13035 6.55000  9 −35.27597 1.00000 1.882997 40.76 10 60.44503 0.1000011 37.37226 5.20000 1.846660 23.78 12 −32.72792 0.82143 13 −23.946281.00000 1.882997 40.76 14 −252.41497 2.00000 1.808090 22.79 15 −72.44788(d15) 16 ∞ 1.00000 Aperture stop S 17 36.72216 3.30000 1.593190 67.87 18−118.19629 0.10000 19 41.37679 3.15000 1.487490 70.41 20 −92.342920.10000 21 42.34033 3.80000 1.487490 70.41 22 −41.00357 1.00000 1.80518125.43 23 259.36092 3.81909 24* −63.64853 1.00000 1.806100 40.94 2522.00000 2.90000 1.805181 25.43 26 150.57815 4.20000 27 −45.824411.00000 1.882997 40.76 28 −215.98952 (d28) 29* 77.17936 3.15000 1.58913061.16 30 −37.11866 0.10000 31 −261.29488 1.00000 1.882997 40.76 3239.98076 4.40000 1.518229 58.93 33 −48.52092 (Bf) I ∞ (AsphericalSurface Data) Surface Number = 6 κ = −5.7774 A4 = 6.79980E−06 A6 =−2.52730E−08 A8 = 8.26150E−11 A10 = −1.02860E−13 Surface Number = 24 κ =2.8196 A4 = 4.59750E−06 A6 = 4.28350E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 29 κ = −6.5363 A4 = −1.95310E−05 A6 =1.79050E−08 A8 = −1.55070E−10 A10 = 4.13770E−13 (Variable Distances) W MT d5 = 2.15153 45.02627 65.69297 d15 = 40.45482 13.14016 2.00000 d28 =8.84506 1.99420 1.50000 Bf = 39.11693 89.39051 99.16649 (Lens GroupData) Group ST Focal Length 1 1 103.25223 2 6 −15.13084 3 16 39.55369(W)35.07124(M) 34.78685(T) 31 16 44.76649 32 29 47.36030 (Values forConditional Expressions)  (3) f1/ft = 0.355  (4) Δ1/f1 = 0.753 (11) ndN= 1.850260 (L11) (12) νdN = 32.35 (L11) (22) ndA″ = 1.497820 (L12) νdA″= 82.52 (L12) (22) ndA″ = 1.593190 (L13) νdA″ = 67.87 (L13) (23) f1/fw =5.569 (24) f1A″/f1 = 1.172 (L12) (24) f1A″/f1 = 1.285 (L13) (25) φ1A″/fw= 2.999 (φ1A″ = 55.60)(L12) (25) φ1A″/fw = 2.918 (φ1A″ = 54.10)(L13)(26) νd3 = 67.87 (L31)

FIGS. 9A, 9B and 9C are graphs showing various aberrations of the zoomlens according to Example 10 of the third embodiment upon focusing on aninfinitely distant object, in which FIG. 9A is a wide-angle end state,FIG. 9B is an intermediate focal length state, and FIG. 9C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example10 of the third embodiment shows superb optical performance as a resultof good corrections to various aberrations.

Example 11

FIG. 10 is a sectional view showing a lens configuration of a zoom lensaccording to Example 11 of the third embodiment of the presentapplication.

As shown in FIG. 10 , the zoom lens according to Example 11 of the thirdembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, a middle lens group G32having negative refractive power, and a rear lens group G33 havingpositive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T,the first lens group G1 is moved monotonously to the object side, thesecond lens group G2 is moved at first to the image side and then to theobject side, and the third lens group G3 is moved monotonously to theobject side with respect to the image plane I such that a distancebetween the first lens group G1 and the second lens group G2 increases,and a distance between the second lens group G2 and the third lens groupG3 decreases. Moreover, the front lens group G31, the middle lens groupG32 and the rear lens group G33 are moved monotonously to the objectside with respect to the image plane I such that a distance between thefront lens group G31 and the middle lens group G32 increases, and adistance between the middle lens group G32 and the rear lens group G33decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by adouble concave negative lens L24 cemented with a double convex positivelens L25. The negative meniscus lens L21 disposed to the most objectside of the second lens group G2 is a compound type aspherical lenswhose object side lens surface is formed as an aspherical surface byapplying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, and a cemented lens constructed by a doubleconvex positive lens L33 cemented with a negative meniscus lens L34having a concave surface facing the object side.

The middle lens group G32 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a double concavenegative lens L41 cemented with a positive meniscus lens L42 having aconvex surface facing the object side, and a negative meniscus lens L43having a concave surface facing the object side. The double concavenegative lens L41 disposed to the most object side of the middle lensgroup G32 is a compound type aspherical lens whose object side lenssurface is an aspherical surface formed by applying a resin layer.

The rear lens group G33 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L51, a doubleconvex positive lens L52, and a cemented lens constructed by a doubleconcave negative lens L53 cemented with a double convex positive lensL54. The double convex positive lens L51 disposed to the most objectside of the rear lens group G33 is a glass mold type aspherical lenswhose object side lens surface is an aspherical surface. Light rays comeout from the double convex positive lens L54 form an image on the imageplane I.

In the zoom lens seen from another point of view according to Example 11of the third embodiment, an antireflection coating described later isapplied to the object side lens surface of the positive meniscus lensL13 in the first lens group G1 and the object side lens surface of thedouble concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to Example 11 ofthe third embodiment are listed in Table 11.

TABLE 11 (Specifications) zoom ratio = 15.701 W M T f = 18.56060104.65150 291.42454 FNO = 3.57565 5.62482 5.81064 ω = 38.80191 7.442052.72113 Y = 14.20 14.20 14.20 TL = 164.76435 225.28899 250.61470 Bf =38.84705 73.57929 86.64770 (Lens Data) i r d nd νd OP ∞ ∞  1 175.605602.20000 1.834000 37.16  2 67.43020 8.80000 1.497820 82.52  3 −587.784800.10000  4 72.27100 6.45000 1.593190 67.87  5 1826.13880  (d5)  6*84.76870 0.10000 1.553890 38.09  7 73.93750 1.20000 1.834807 42.72  817.18730 6.95000  9 −36.98220 1.00000 1.816000 46.62 10 77.92630 0.1500011 36.63460 5.30000 1.784723 25.68 12 −36.63460 0.80000 13 −26.199101.00000 1.816000 46.62 14 63.73960 2.05000 1.808090 22.79 15 −643.27060(d15) 16 ∞ 1.00000 Aperture Stop S 17 65.83650 3.40000 1.593190 67.87 18−50.15460 0.10000 19 65.68170 2.45000 1.487490 70.41 20 −154.974300.10000 21 46.73330 4.20000 1.487490 70.41 22 −35.78330 1.00000 1.80809022.79 23 −191.93180 (d23) 24* −57.29660 0.20000 1.553890 38.09 25−59.72500 0.90000 1.696797 55.52 26 28.51000 2.15000 1.728250 28.46 2791.99760 4.14020 28 −32.89540 1.00000 1.729157 54.66 29 −144.33150 (d29)30* 6427.19190 4.65000 1.589130 61.18 31 −27.38180 0.10000 32 31.477605.85000 1.487490 70.41 33 −43.75390 1.45000 34 −113.58970 1.000001.882997 40.76 35 20.34810 5.30000 1.548141 45.79 36 −709.14530 (Bf) I ∞(Aspherical Surface Data) Surface Number = 6 κ = 1.0000 A4 = 2.88220E−06A6 = −2.29350E−11 A8 = −2.35280E−11 A10 = 9.21570E−14 Surface Number =24 κ = 1.0000 A4 = 4.32780E−06 A6 = 1.88460E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 30 κ = 1.0000 A4 = −1.36170E−05 A6 =−3.55860E−10 A8 = 1.83080E−11 A10 = −1.86790E−13 (Variable Distances) WM T d5 = 2.15700 53.01000 76.25220 d15 = 33.36360 11.30360 2.00000 d23 =3.46820 9.64300 9.62460 d29 = 11.83830 2.66290 1.00000 Bf = 38.8470573.57929 86.64770 (Lens Group Data) Group ST Focal Length 1 1 117.729372 6 −15.60945 3 16 40.44471(W) 33.95695(M) 32.70088(T) 31 16 27.35473 3224 −26.50041 33 30 35.20423 (Values for Conditional Expressions)  (3)f1/ft = 0.404  (4) Δ1/f1 = 0.729 (11) ndN = 1.834000 (L11) (12) νdN =37.16 (L11) (22) ndA″ = 1.497820 (L12) νdA″ = 82.52 (L12) (22) ndA″ =l.593190 (L13) νdA″ = 67.87 (L13) (23) f1/fw = 6.343 (24) f1A″/f1 =1.037 (L12) (24) f1A″/f1 = 1.076 (L13) (25) φ1A″/fw = 3.081 (φ1A″ =57.19)(L12) (25) φ1A″/fw = 2.909 (φ1A″ = 54.00)(L13) (26) νd3 = 67.87(L31)

FIGS. 11A, 11B and 11C are graphs showing various aberrations of thezoom lens according to Example 11 of the third embodiment upon focusingon an infinitely distant object, in which FIG. 11A is a wide-angle endstate, FIG. 11B is an intermediate focal length state, and FIG. 11C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example11 of the third embodiment shows superb optical performance as a resultof good corrections to various aberrations.

Example 12

FIG. 15 is a sectional view showing a lens configuration of a zoom lensaccording to Example 12 of the third embodiment of the presentapplication.

As shown in FIG. 15 , the zoom lens according to Example 12 of the thirdembodiment is composed of, in order from an object side along an opticalaxis, a first lens group G1 having positive refractive power, a secondlens group G2 having negative refractive power, and a third lens groupG3 having positive refractive power. The third lens group G3 is composedof, in order from the object side along the optical axis, a front lensgroup G31 having positive refractive power, and a rear lens group G32having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, thefirst lens group G1 is moved monotonously to the object side, the secondlens group G2 is moved at first to the image side and then to the objectside, and the third lens group G3 is moved monotonously to the objectside with respect to the image plane I such that a distance between thefirst lens group G1 and the second lens group G2 increases, and adistance between the second lens group G2 and the third lens group G3decreases. Moreover, the front lens group G31, and the rear lens groupG32 are moved monotonously to the object side with respect to the imageplane I such that a distance between the front lens group G31 and therear lens group G32 decreases.

An aperture stop S is disposed to the most object side of the third lensgroup G3, which is disposed to the image side of the second lens groupG2, and formed in a body with the front lens group G31.

The first lens group G1 is composed of, in order from the object sidealong the optical axis, a cemented lens constructed by a negativemeniscus lens L11 having a convex surface facing the object sidecemented with a double convex positive lens L12, and a positive meniscuslens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object sidealong the optical axis, a negative meniscus lens L21 having a convexsurface facing the object side, a double concave negative lens L22, adouble convex positive lens L23, and a cemented lens constructed by anegative meniscus lens L24 having a convex surface facing the image sidecemented with a positive meniscus lens L25 having a convex surfacefacing the image side. The negative meniscus lens L21 disposed to themost object side of the second lens group G2 is a compound typeaspherical lens whose object side lens surface is formed as anaspherical surface by applying a resin layer.

The front lens group G31 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L31, a doubleconvex positive lens L32, a cemented lens constructed by a double convexpositive lens L33 cemented with a double concave negative lens L34, acemented lens constructed by a double concave negative lens L35 cementedwith a double convex positive lens L36, and a negative meniscus lens L37having a concave surface facing the object side. The double concavenegative lens L35 is a glass mold type aspherical lens whose object sidelens surface is formed as an aspherical surface.

The rear lens group G32 is composed of, in order from the object sidealong the optical axis, a double convex positive lens L41, and acemented lens constructed by a negative meniscus lens L42 having aconvex surface facing the object side cemented with a double convexpositive lens L43. The double convex positive lens L41 disposed to themost object side of the rear lens group G32 is a glass mold typeaspherical lens whose object side lens surface is an aspherical surface.Light rays come out from the double convex positive lens L43 form animage on the image plane I.

In the zoom lens seen from another point of view according to Example 12of the third embodiment, an antireflection coating described later isapplied to the image side lens surface of the double convex positivelens L12 in the first lens group G1 and the image side lens surface ofthe negative meniscus lens L21 in the second lens group G2.

Various values associated with the zoom lens according to Example 12 ofthe third embodiment are listed in Table 12.

TABLE 12 (Specifications) zoom ratio = 15.698 W M T f = 18.53928105.00169 291.02949 FNO = 3.60631 5.76130 5.78825 ω = 39.00856 7.485102.73699 Y = 14.20 14.20 14.20 TL = 148.79923 217.34659 242.82932 Bf =39.00067 91.11965 105.34665 (Lens Data) i r d nd νd OP ∞ ∞  1 127.944472.00000 1.850260 32.35  2 66.54596 7.85000 1.497820 82.52  3 −596.230690.10000  4 67.44029 5.40000 1.593190 67.87  5 436.18989  (d5)  6*135.29609 0.15000 1.553890 38.09  7 107.25966 1.00000 1.804000 46.58  815.26261 6.70000  9 −34.54986 1.00000 1.834807 42.72 10 51.89897 0.1000011 34.09670 4.50000 1.784723 25.68 12 −32.12451 0.90000 13 −21.115691.00000 1.882997 40.76 14 −2390.20620 2.10000 1.922860 20.50 15−67.61249 (d15) 16 ∞ 1.00000 Aperture Stop S 17 31.61335 3.650001.593190 67.87 18 −218.55454 0.10000 19 49.13044 3.20000 1.487490 70.4120 −63.62105 0.10000 21 35.35729 4.25000 1.487490 70.41 22 −34.078261.00000 1.846660 23.78 23 659.96058 3.90000 24* −35.03665 1.000001.756998 47.82 25 17.58221 3.90000 1.698947 30.13 26 −95.26227 3.3500027 −55.52002 1.00000 1.882997 40.7 6 28 −585.51718 (d28) 29* 439.793462.20000 1.589130 61.16 30 −53.20688 0.10000 31 65.13402 1.00000 1.83400037.16 32 27.72956 4.10000 1.487490 70.41 33 −58.13289 (Bf) I ∞(Aspherical Surface Data) Surface Number = 6 κ = 4.3350 A4 = 9.45630E−06A6 = −1.51470E−08 A8 = −1.16860E−12 A10 = 1.65790E−13 Surface Number =24 κ = −0.3009 A4 = 6.23810E−06 A6 = 8.96820E−09 A8 = 0.00000E+00 A10 =0.00000E+00 Surface Number = 29 κ = −20.0000 A4 = −1.92960E−05 A6 =5.96200E−09 A8 = −1.65600E−10 A10 = 4.18100E−13 (Variable Distances) W MT d5 = 2.10000 46.65937 67.33267 d15 = 33.50310 10.98454 2.00000 d28 =7.54546 1.93303 1.50000 Bf = 39.00067 91.11965 105.34665 (Lens GroupData) Group ST Focal Length 1 1 104.30654 2 6 −13.81152 3 16 36.15068(W)32.66171(M) 32.42030(T) 31 16 39.54020 32 29 48.03635 (Values forConditional Expressions)  (3) f1/ft = 0.358  (4) Δ1/f1 = 0.901 (11) ndN= 1.850260 (L11) (12) νdN = 32.35 (L11) (22) ndA″ = 1.497820 (L12) νdA″= 82.52 (L12) (22) ndA″ = 1.593190 (L13) νdA″ = 67.87 (L13) (23) f1/fw =5.626 (24) f1A″/f1 = 1.157 (L12) (24) f1A″/f1 = 1.282 (L13) (25) φ1A″/fw= 2.982 (φ1A″ = 55.29)(L12) (25) φ1A″/fw = 2.919 (φ1A″ = 54.12)(L13)(26) νd3 = 67.87 (L31)

FIGS. 16A, 16B and 16C are graphs showing various aberrations of thezoom lens according to Example 12 of the third embodiment upon focusingon an infinitely distant object, in which FIG. 16A is a wide-angle endstate, FIG. 16B is an intermediate focal length state, and FIG. 16C is atelephoto end state.

As is apparent from various graphs, the zoom lens according to Example12 of the third embodiment shows superb optical performance as a resultof good corrections to various aberrations.

Then, an outline of a method for manufacturing a zoom lens according tothe third embodiment is explained.

FIG. 26 is a flowchart schematically explaining a method formanufacturing the zoom lens according to the third embodiment.

The method for manufacturing a zoom lens according to the thirdembodiment is a method for manufacturing a zoom lens including, in orderfrom an object side along an optical axis, a first lens group G1 havingpositive refractive power, a second lens group G2 having negativerefractive power, and a third lens group G3 having positive refractivepower, and being constructed such that at least one optical surface inthe first lens group and the second lens group is applied with anantireflection coating, and the antireflection coating includes at leastone layer that is formed by a wet process, the method including stepsS31 through S33 shown in FIG. 26 .

Step S31: disposing the first lens group G1, the second lens group G2and the third lens group G3 movably such that upon zooming from awide-angle end state to a telephoto end state, a distance between thefirst lens group and the second lens group increases, and a distancebetween the second lens group and the third lens group decreases.

Step S32: disposing a plurality of positive lenses satisfying thefollowing conditional expression (22) into the first lens group:66.5<νdA″ when 1.540≤ndA″75.0<νdA″ when ndA″≤1.540  (22)where ndA″ denotes a refractive index at d-line (wavelength λ=587.6 nm)of a material of each of a plurality of positive lenses in the firstlens group, and νdA″ denotes an Abbe number at d-line (wavelengthλ=587.6 nm) of a material of each of a plurality of positive lenses inthe first lens group.

Step S33: disposing each lens with satisfying the following conditionalexpressions (23) and (3):4.75<f1/fw<11.0  (23)0.28<f1/ft<0.52  (3)where fw denotes a focal length of the zoom lens in the wide-angle endstate, ft denotes a focal length of the zoom lens in the telephoto endstate, and f1 denotes a focal length of the first lens group.

With this method for manufacturing a zoom lens according to the thirdembodiment, it becomes possible to manufacture a zoom lens havingexcellent optical performance with suppressing variations in aberrationsand ghost images and flare.

Then, an antireflection coating used in the zoom lens seen from anotherpoint of view according to each Example of the first through thirdembodiments is explained.

FIG. 17 is an explanatory view showing a configuration of anantireflection coating (which is also referred to as a multilayerbroadband antireflection coating) used in the zoom lens according to thepresent embodiment. The antireflection coating 101 is composed of sevenlayers and is formed on an optical surface of an optical member 102 suchas a lens. A first layer 101 a is formed with aluminum oxide by means ofa vacuum evaporation method. On the first layer 101 a, a second layer101 b formed with mixture of titanium oxide and zirconium oxide by meansof a vacuum evaporation method is formed. Moreover, on the second layer101 b, a third layer 101 c formed with aluminum oxide by means of vacuumevaporation method is formed. Moreover, on the third layer 101 c, afourth layer 101 f formed with a mixture of titanium oxide and zirconiumoxide by means of a vacuum evaporation method is formed. Furthermore, onthe fourth layer 101 d, a fifth layer 101 e formed with aluminum oxideby means of vacuum evaporation method is formed. On the fifth layer 101e, a sixth layer 101 f formed with mixture of titanium oxide andzirconium oxide by means of a vacuum evaporation method is formed.

Then, on the sixth layer 101 f formed in this manner, a seventh layer101 g formed with a mixture of silica and magnesium fluoride is formedby means of a wet process to form the antireflection coating accordingto the present embodiment. In order to form the seventh layer 101 g, asol-gel process, which is a kind of wet process, is used. The sol-gelprocess is a process of transforming a sol acquired by mixing a materialinto a gel having no fluidity through hydrolyzing condensationpolymerization reaction and acquiring a product by heat-decomposing thisgel. In manufacturing an optical thin film, the film may be generated bycoating a material sol of the optical thin film over the optical surfaceof the optical member and dry-solidifying the sol into a gel film. Notethat the wet process may involve using, without being limited to thesol-gel process, a process of acquiring a solid-state film through noneof the gel state.

In this manner, the first layer 101 a through the sixth layer 101 f areformed by electron beam evaporation, which is a dry process, and theseventh layer 101 g, which is the uppermost layer, is formed by afollowing wet-process using sol liquid prepared by a hydrofluoricacid/magnesium acetate method. At first, an aluminum oxide layer, whichbecomes a first layer 101 a, a mixture of titanium oxide and zirconiumoxide layer, which becomes a second layer 101 b, an aluminum oxidelayer, which becomes a third layer 101 a, a mixture of titanium oxideand zirconium oxide layer, which becomes a fourth layer 101 b, analuminum oxide layer, which becomes a fifth layer 101 a, and a mixtureof titanium oxide and zirconium oxide layer, which becomes a sixth layer101 b are formed on a film-forming surface (the above-mentioned opticalsurface of the optical member 102) in this order by a vacuum evaporationequipment. Then, after being took out from the vacuum evaporationequipment, the optical member 102 is applied with a sol liquid preparedby the hydrofluoric acid/magnesium acetate method by means of a spincoat method, so that a layer formed by a mixture of silica and magnesiumfluoride, which becomes a seventh layer 101 g, is formed. A reactionformula prepared by the hydrofluoric acid/magnesium acetate method isshown by expression (a):2HF+Mg(CH3COO)2→MgF2+2CH3COOH  (a).

The sol liquid is used for forming the film after mixing ingredientswith undergoing high temperature, high pressure maturing process at 140°C., 24 hours by means of an autoclave. After completion of forming theseventh layer 101 g, the optical member 102 is processed with heatingtreatment at 160° C. in atmospheric pressure for 1 hour to be completed.With using such a sol gel method, atoms or molecules are built up fromseveral to several tens to become particles of several nanometers toseveral tens of nanometers, and several these particles are built up toform secondary particles. As a result, the secondary particles are piledup to form the seventh layer 101 g.

Optical performance of the optical member including the thus-formedantireflection coating 101 will hereinafter be described by usingspectral characteristics shown in FIG. 18 .

The optical member (lens) including the antireflection coating accordingto each of the first through third embodiments is formed under theconditions shown in the following Table 13. Herein, the Table 13 showsrespective optical film thicknesses of the layers 101 a (the firstlayer) through 101 g (the seventh layer) of the antireflection coating101, which are obtained under such conditions that λ denotes a referencewavelength and the refractive index of the substrate (optical member) isset to 1.62, 1.74 and 1.85. Note that the Table 13 shows Al2O3 expressedas the aluminum oxide, ZrO2+TiO2 expressed as the mixture of titaniumoxide and zirconium oxide and MgF2+SiO2 expressed as the mixture ofmagnesium fluoride and silica.

TABLE 13 layer material n thicknesses of layers medium air 1 7 MgF2 +SiO2 1.26 0.268λ 0.271λ 0.269λ 6 ZrO2 + TiO2 2.12 0.057λ 0.054λ 0.059λ 5Al2O3 1.65 0.171λ 0.178λ 0.162λ 4 ZrO2 + TiO2 2.12 0.127λ 0.13λ 0.158λ 3Al2O3 1.65 0.122λ 0.107λ 0.08λ 2 ZrO2 + TiO2 2.12 0.059λ 0.075λ 0.105λ 1Al2O3 1.65 0.257λ 0.03λ 0.03λ n (substrate) 1.62 1.74 1.85

FIG. 18 shows the spectral characteristics when the light beamsvertically are incident on the optical member in which the optical filmthickness of each of the layers of the antireflection coating 101 isdesigned, with the reference wavelength A set to 550 nm in Table 13.

It is understood from FIG. 18 that the optical member including theantireflection coating 101 designed with the reference wavelength A setto 550 nm can restrain the reflectance down to 0.2% or less over theentire range in which the wavelengths of the light beams are 420 nmthrough 720 nm. Further, in the Table 13, even the optical memberincluding the antireflection coating 101, in which each optical filmthickness is designed with the reference wavelength A set to the d-line(wavelength 587.6 nm), has substantially the same spectralcharacteristics as in the case where the reference wavelength A shown inFIG. 18 is 550 nm in a way that affects substantially none of thespectral characteristics thereof.

Next, a modified example of the antireflection coating will beexplained. The antireflection coating is a 5-layered film, and,similarly to the Table 13, the optical film thickness of each layer withrespect to the reference wavelength A is designed under conditions shownin the following Table 14. In this modified example, the formation ofthe fifth layer involves using the sol-gel process described above.

TABLE 14 layer material n thicknesses of layers medium air 1 5 MgF2 +SiO2 1.26 0.275λ 0.269λ 4 ZrO2 + TiO2 2.12 0.045λ 0.043λ 3 Al2O3 1.650.212λ 0.217λ 2 ZrO2 + TiO2 2.12 0.077λ 0.066λ 1 Al2O3 1.65 0.288λ0.290λ n (substrate) 1.46 1.52

FIG. 19 shows the spectral characteristics when the light beamsvertically are incident on the optical member in which the optical filmthickness of each of the layers is designed, with the substraterefractive index set to 1.52 and the reference wavelength A set to 550nm in the Table 14. It is understood from FIG. 19 that theantireflection coating in the modified example can restrain thereflectance down to 0.2% or under over the entire range in which thewavelengths of the light beams are 420 nm-720 nm. Note that in the Table14, even the optical member including the antireflection coating, inwhich each optical film thickness is designed with the referencewavelength A set to the d-line (wavelength 587.6 nm), has substantiallythe same spectral characteristics as the spectral characteristics shownin FIG. 19 in a way that affects substantially none of the spectralcharacteristics thereof.

FIG. 20 shows the spectral characteristics in such a case that theincident angles of the light beams upon the optical member having thespectral characteristics shown in FIG. 19 are 30 degrees, 45 degrees and60 degrees, respectively. Note that FIGS. 19 and 20 do not illustratethe spectral characteristics of the optical member including theantireflection coating in which the substrate refractive index is 1.46shown in Table 14, however, it is understood that the optical member hassubstantially the same spectral characteristics such as the substraterefractive index being 1.52.

Furthermore, FIG. 21 shows one example of the antireflection coatinggrown by only the dry process such as the conventional vacuumevaporation method by way of a comparison. FIG. 21 shows the spectralcharacteristics when the light beams are incident on the optical memberin which to design the antireflection coating structured under theconditions shown in the following Table 13, with the substraterefractive index set to 1.52 in the same way as in the Table 12.Moreover, FIG. 22 shows the spectral characteristics in such a case thatthe incident angles of the light beams upon the optical member havingthe spectral characteristics shown in FIG. 21 are 30 degrees, 45 degreesand 60 degrees, respectively.

TABLE 15 layer material n thicknesses of layers medium air 1 7 MgF2 1.390.243λ 6 ZrO2 + TiO2 2.12 0.119λ 5 Al2O3 1.65 0.057λ 4 ZrO2 + TiO2 2.120.220λ 3 Al2O3 1.65 0.064λ 2 ZrO2 + TiO2 2.12 0.057λ 1 Al2O3 1.65 0.193λrefractive index of substrate 1.52

To compare the spectral characteristics of the optical member includingthe antireflection coating according to the present embodimentillustrated in FIGS. 18 through 20 with the spectral characteristics inthe conventional examples shown in FIGS. 21 and 22 , it is wellunderstood that the present antireflection coating has the much lowerreflectance at any incident angles and, besides, has the low reflectancein the broader band.

Then, an example of applying the antireflection coating shown in theTable 13 to Examples 1 of the first embodiment through Example 12 of thethird embodiment discussed above is explained.

In the zoom lens seen from another point of view according to Example 1of the first embodiment, as shown in the Table 1, the refractive indexnd of the negative meniscus lens L21 of the second lens group G2 is1.834807 (nd=1.834807), and the refractive index nd of the doubleconcave negative lens L22 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.85 as the substrate refractive index to the image side lens surface ofthe negative meniscus lens L21 and applying the antireflection coating(see Table 13) corresponding to 1.85 as the substrate refractive indexto the object side lens surface of the double concave negative lens L22.

In the zoom lens seen from another point of view according to Example 2of the first embodiment, as shown in the Table 2, the refractive indexnd of the positive meniscus lens L13 of the first lens group G1 is1.603001 (nd=1.603001), and the refractive index nd of the double convexpositive lens L23 of the second lens group G2 is 1.846660 (nd=1.846660),whereby it is feasible to reduce the reflected light from each lenssurface and to reduce ghost images and flare as well by applying theantireflection coating 101 (see Table 13) corresponding to 1.62 as thesubstrate refractive index to the object side lens surface of thepositive meniscus lens L13 and applying the antireflection coating (seeTable 13) corresponding to 1.85 as the substrate refractive index to theimage side lens surface of the double convex positive lens L23.

In the zoom lens seen from another point of view according to Example 3of the first embodiment, as shown in the Table 3, the refractive indexnd of the double convex positive lens L12 of the first lens group G1 is1.437000 (nd=1.437000), and the refractive index nd of the doubleconcave negative lens L24 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 14) corresponding to1.46 as the substrate refractive index to the image side lens surface ofthe double convex positive lens L12 and applying the antireflectioncoating (see Table 13) corresponding to 1.85 as the substrate refractiveindex to the object side lens surface of the double concave negativelens L24.

In the zoom lens seen from another point of view according to Example 4of the second embodiment, as shown in the Table 4, the refractive indexnd of the negative meniscus lens L21 of the second lens group G2 is1.834807 (nd=1.834807), and the refractive index nd of the doubleconcave negative lens L22 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.85 as the substrate refractive index to the image side lens surface ofthe negative meniscus lens L21 and applying the antireflection coating(see Table 13) corresponding to 1.85 as the substrate refractive indexto the object side lens surface of the double concave negative lens L22.

In the zoom lens seen from another point of view according to Example 5of the second embodiment, as shown in the Table 5, the refractive indexnd of the positive meniscus lens L13 of the first lens group G1 is1.593190 (nd=1.593190), and the refractive index nd of the double convexpositive lens L23 of the second lens group G2 is 1.846660 (nd=1.846660),whereby it is feasible to reduce the reflected light from each lenssurface and to reduce ghost images and flare as well by applying theantireflection coating 101 (see Table 13) corresponding to 1.62 as thesubstrate refractive index to the object side lens surface of thepositive meniscus lens L13 and applying the antireflection coating (seeTable 13) corresponding to 1.85 as the substrate refractive index to theimage side lens surface of the double convex positive lens L23.

In the zoom lens seen from another point of view according to Example 6of the second embodiment, as shown in the Table 6, the refractive indexnd of the positive meniscus lens L13 of the first lens group G1 is1.593190 (nd=1.593190), and the refractive index nd of the doubleconcave negative lens L24 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.62 as the substrate refractive index to the object side lens surfaceof the positive meniscus lens L13 and applying the antireflectioncoating (see Table 13) corresponding to 1.85 as the substrate refractiveindex to the object side lens surface of the double concave negativelens L24.

In the zoom lens seen from another point of view according to Example 7of the second embodiment, as shown in the Table 7, the refractive indexnd of the negative meniscus lens L21 of the second lens group G2 is1.834810 (nd=1.834810), and the refractive index nd of the doubleconcave negative lens L22 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.85 as the substrate refractive index to the image side lens surface ofthe negative meniscus lens L21 and applying the antireflection coating(see Table 13) corresponding to 1.85 as the substrate refractive indexto the object side lens surface of the double concave negative lens L22.

In the zoom lens seen from another point of view according to Example 8of the second embodiment, as shown in the Table 8, the refractive indexnd of the double convex positive lens L12 of the first lens group G1 is1.437000 (nd=1.437000), and the refractive index nd of the doubleconcave negative lens L24 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 14) corresponding to1.46 as the substrate refractive index to the image side lens surface ofthe double convex positive lens L12 and applying the antireflectioncoating (see Table 13) corresponding to 1.85 as the substrate refractiveindex to the object side lens surface of the double concave negativelens L24.

In the zoom lens seen from another point of view according to Example 9of the third embodiment, as shown in the Table 9, the refractive indexnd of the negative meniscus lens L21 of the second lens group G2 is1.834810 (nd=1.834810), and the refractive index nd of the doubleconcave negative lens L22 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.85 as the substrate refractive index to the image side lens surface ofthe negative meniscus lens L21 and applying the antireflection coating(see Table 13) corresponding to 1.85 as the substrate refractive indexto the object side lens surface of the double concave negative lens L22.

In the zoom lens seen from another point of view according to Example 10of the third embodiment, as shown in the Table 10, the refractive indexnd of the positive meniscus lens L13 of the first lens group G1 is1.593190 (nd=1.593190), and the refractive index nd of the double convexpositive lens L23 of the second lens group G2 is 1.846660 (nd=1.846660),whereby it is feasible to reduce the reflected light from each lenssurface and to reduce ghost images and flare as well by applying theantireflection coating 101 (see Table 13) corresponding to 1.62 as thesubstrate refractive index to the object side lens surface of thepositive meniscus lens L13 and applying the antireflection coating (seeTable 13) corresponding to 1.85 as the substrate refractive index to theimage side lens surface of the double convex positive lens L23.

In the zoom lens seen from another point of view according to Example 11of the third embodiment, as shown in the Table 11, the refractive indexnd of the positive meniscus lens L13 of the first lens group G1 is1.593190 (nd=1.593190), and the refractive index nd of the doubleconcave negative lens L24 of the second lens group G2 is 1.816000(nd=1.816000), whereby it is feasible to reduce the reflected light fromeach lens surface and to reduce ghost images and flare as well byapplying the antireflection coating 101 (see Table 13) corresponding to1.62 as the substrate refractive index to the object side lens surfaceof the positive meniscus lens L13 and applying the antireflectioncoating (see Table 13) corresponding to 1.85 as the substrate refractiveindex to the object side lens surface of the double concave negativelens L24.

In the zoom lens seen from another point of view according to Example 12of the third embodiment, as shown in the Table 12, the refractive indexnd of the double convex positive lens L12 of the first lens group G1 is1.497820 (nd=1.497820), and the refractive index nd of the negativemeniscus lens L21 of the second lens group G2 is 1.804000 (nd=1.804000),whereby it is feasible to reduce the reflected light from each lenssurface and to reduce ghost images and flare as well by applying theantireflection coating 101 (see Table 13) corresponding to 1.52 as thesubstrate refractive index to the image side lens surface of the doubleconvex positive lens L12 and applying the antireflection coating (seeTable 13) corresponding to 1.85 as the substrate refractive index to theimage side lens surface of the negative meniscus lens L21.

As described above, the first embodiment through the third embodimentmake it possible to provide a zoom lens having high optical performancewith suppressing variations in aberrations.

Then, a camera, which is an optical apparatus equipped with the zoomlens according to the first embodiment, is explained. Although a casethat the zoom lens according to Example 1 of the first embodiment isinstalled is explained, the same result can be obtained by a zoom lensaccording to any other Examples according to first embodiment throughthe third embodiment.

FIG. 23 is a sectional view showing a single-lens reflex digital cameraequipped with the zoom lens according to Example 1 of the firstembodiment.

In FIG. 23 , the camera 1 is a single-lens reflex digital camera 1equipped with the zoom lens according to Example 1 of the firstembodiment as an imaging lens 2. In the camera 1, light rays emittedfrom an unillustrated object are converged by the imaging lens 2,reflected by a quick return mirror 3, and focused on a focusing screen4. The light rays focused on the focusing screen 4 are reflected aplurality of times in a pentagonal roof prism 5, and led to an eyepiece6. Accordingly, a photographer can observe the object image as anerected image through the eyepiece 6.

When the photographer presses an unillustrated release button all theway down, the quick return mirror 3 is retracted from the optical path,the light rays from the unillustrated object are formed an object imageon an imaging device 7. Accordingly, the light rays emitted from theobject are captured by the imaging device 7, and stored in anunillustrated memory as a photographed image of the object. In thismanner, the photographer can take a picture of an object by the camera1.

With installing the zoom lens according to Example 1 of the firstembodiment as an imaging lens 2 into the camera 1, it becomes possibleto realize a camera having high optical performance.

Incidentally, the same effect as the above described camera 1 can beobtained by a camera including none of the quick return mirror 3.

Incidentally, the following description may suitably be applied withinlimits that do not deteriorate optical performance.

In the above described explanations and Examples, although zoom lenseshaving a three-lens-group configuration have been shown, the presentapplication can be applied to other lens configurations such as afour-lens-group configuration. Specifically, a lens configuration inwhich a lens or a lens group is added to the most object side, or themost image side of the zoom lens is possible. Incidentally, a lens groupis defined as a portion including at least one lens separated by airspaces that vary upon zooming.

In a zoom lens according to the present application, in order to varyfocusing from infinitely distant object to a close object, a portion ofa lens group, a single lens group, or a plurality of lens groups may bemoved along the optical axis as a focusing lens group. In this case, thefocusing lens group can be used for auto focus, and suitable for beingdriven by a motor such as an ultrasonic motor. It is particularlypreferable that at least a portion of the second lens group is moved asthe focusing lens group.

Moreover, in a zoom lens according to the present application, a lensgroup or a portion of a lens group may be moved as a vibration reductionlens group in a direction including a component perpendicular to theoptical axis, or tilted (swayed) in a direction including the opticalaxis thereby correcting an image blur caused by a camera shake. Inparticular, at least a portion of the third lens group is preferablymade as the vibration reduction lens group.

In a zoom lens according to the present application, any lens surfacemay be a spherical surface, a plane surface, or an aspherical surface.

When a lens surface is a spherical surface or a plane surface, lensprocessing, assembling and adjustment become easy, and deterioration inoptical performance caused by lens processing, assembling and adjustmenterrors can be prevented, so that it is preferable. Moreover, even if theimage plane is shifted, deterioration in optical performance is little,so that it is preferable.

When a lens surface is an aspherical surface, the aspherical surface maybe fabricated by a fine grinding process, a glass molding process that aglass material is formed into an aspherical shape by a mold, or acompound type process that a resin material is formed into an asphericalshape on a glass lens surface. A lens surface may be a diffractiveoptical surface, and a lens may be a graded-index type lens (GRIN lens)or a plastic lens.

In a zoom lens according to the present application, the zoom ratio isabout 7 to 25.

In a zoom lens according to the present application, the first lensgroup preferably includes two positive lens components. The first lensgroup preferably disposes these lens components, in order from theobject side, positive-positive with disposing an air space between them.

Moreover, the second lens group preferably includes one positive lenscomponent and three negative lens components. The second lens grouppreferably disposes these lens components, in order from the objectside, negative-negative-positive-negative with disposing air spacesbetween them.

Moreover, the third lens group preferably includes at least threepositive lens components and at least one negative lens component.

Moreover, the third lens group preferably includes six or seven positivelens components and three or four negative lens components.

The above described Examples of each embodiment of the presentapplication only show a specific example for the purpose of betterunderstanding of the present application. Accordingly, it is needless tosay that the present application in its broader aspect is not limited tothe specific details and representative devices.

What is claimed is:
 1. A zoom lens comprising, in order from an objectalong an optical axis: a first lens group having positive refractivepower; a second lens group having negative refractive power; and a thirdlens group having positive refractive power, upon zooming from awide-angle end state to a telephoto end state, a distance between thefirst lens group and the second lens group increasing, and a distancebetween the second lens group and third lens group decreasing, the zoomlens including a positive lens A that satisfies the followingconditional expressions:1.540<ndA66.5<νdA where ndA denotes a refractive index at d-line of a material ofthe positive lens A, and νdA denotes an Abbe number at d-line of thematerial of the positive lens A, and the first lens group including anegative lens N that satisfies the following conditional expression:1.904=<ndN where ndN denotes a refractive index at d-line of a materialof the negative lens N in the first lens group.
 2. The zoom lensaccording to claim 1, wherein the following conditional expression issatisfied:0.25<Δ1/f1<1.10 where Δ1 denotes a moving amount of the first lens groupwith respect to an image plane from the wide-angle end state to thetelephoto end state, and f1 denotes a focal length of the first lensgroup.
 3. The zoom lens according to claim 1, wherein the first lensgroup includes two positive lenses.
 4. The zoom lens according to claim1, wherein the number of the negative lens N in the first lens group isone.
 5. The zoom lens according to claim 1, wherein the third lens groupincludes, in order from the object side along the optical axis, a frontgroup having positive refractive power, a middle group having negativerefractive power and a rear group having positive refractive power, andupon zooming from the wide-angle end state to the telephoto end state, adistance between the front group and the middle group varying, and adistance between the middle group and rear group varying.
 6. The zoomlens according to claim 5, wherein the front group includes the positivelens A.
 7. The zoom lens according to claim 6, wherein the followingconditional expression is satisfied:0.55<f31A/f31<2.45 where f31 denotes a focal length of the front group,and f31A denotes a focal length of the positive lens A in the frontgroup.
 8. The zoom lens according to claim 1, wherein the third lensgroup consists of, in order from the object along the optical axis, afront group having positive refractive power, a middle group havingnegative refractive power and a rear group having positive refractivepower, and upon zooming from the wide-angle end state to the telephotoend state, the front group, the middle group and the rear group movealong the optical axis.
 9. The zoom lens according to claim 8, wherein,upon zooming from the wide-angle end state to the telephoto end state,the first lens group and the second lens group move along the opticalaxis.
 10. A zoom lens comprising, in order from an object along anoptical axis: a first lens group having positive refractive power; asecond lens group having negative refractive power; and a third lensgroup having positive refractive power, upon zooming from a wide-angleend state to a telephoto end state, a distance between the first lensgroup and the second lens group increasing, and a distance between thesecond lens group and third lens group decreasing, the zoom lensincluding a positive lens A that satisfies the following conditionalexpressions:1.540<ndA66.5<νdA where ndA denotes a refractive index at d-line of a material ofthe positive lens A, and νdA denotes an Abbe number at d-line of thematerial of the positive lens A, and the zoom lens satisfying thefollowing conditional expression:0.25<Δ1/f1<1.10 where Δ1 denotes a moving amount of the first lens groupwith respect to an image plane from the wide-angle end state to thetelephoto end state, and f1 denotes a focal length of the first lensgroup.
 11. The zoom lens according to claim 10, wherein the third lensgroup consists of, in order from the object side along the optical axis,a front group having positive refractive power, a middle group havingnegative refractive power and a rear group having positive refractivepower, and upon zooming from the wide-angle end state to the telephotoend state, the front group, the middle group and the rear group movealong the optical axis.
 12. The zoom lens according to claim 11,consisting of the first lens group, the second lens group, the frontgroup, the middle group and the rear group, and upon zooming from thewide-angle end state to the telephoto end state, the first lens group,the second lens group, the front group, the middle group and the reargroup moving along the optical axis.